Light Metals Permanent Mold Casting - E-smarrt.org
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Summary of Light Metals Permanent Mold Casting - E-smarrt.org
Final Technical Report Project Title: Light Metals Permanent Mold Casting Award Number: DE-FC36-04GO14230 Project Period: January 2004 – March 31, 2014 Principal Investigator(s): Yemi Fasoyinu, 905-645-0779, [email protected] Recipient Organization: CanmetMATERIALS, Natural Resources Canada 183 Longwood Road South, Hamilton, ON, L8P 0A5, Canada Laboratory Former Address: CANMET MTL (Materials Technology Laboratory), Natural Resources Canada 568 Booth Street, Ottawa, ON, KIA 0G1, Canada Participants (cost sharing): January 2004 – June 30, 2009 Eck Industries, Inc. Grenville Castings Limited Magma Foundry Technologies, Inc. Alcan International Ltd. Participants (cost sharing): June 2012 – March 31, 2014 Eck Industries, Inc. B.S Metallurgy, Inc. Product Development &Analysis (PDA) LLC March 2014 1
Acknowledgment, Disclaimer and Proprietary Data Notice Acknowledgment: This report is based upon work supported by the U. S. Department of Energy under Award No.DE-FC36-04GO14230 Disclaimer: Any findings, opinions, and conclusions or recommendations expressed in this report are those of the author(s) and do not necessarily reflect the views of the Department of Energy. Proprietary Data Notice: None in report i
Table of Contents List of Figures iv List of Tables vi 1 Executive Summary 1 2 Introduction 2 3. Background 3 3.1 Specific Goals and Objectives 4 TASK 1 - Selection of Prototype Component 4 TASK 2 - Hot Tearing Studies 4 TASK 3 – Prototype Casting Trials (at CANMET) 4 TASK 4 – Mechanical Properties and Metallographic Evaluation 4 TASK 5 - Technology Transfer 4 3.2 Team Members 5 4 Results and Discussion 6 4.1 TASK 1: Selection of Prototype Components 6 4.1.1 Regular Restrained Mold 6 4.1.2 Instrumented Restrained Mold 6 4.1.3 Engine Mount Casting 8 4.1.4 Rocker Arm Casting 8 4.2 TASK 2 - Hot Tearing and Computer Simulation Studies 9 4.2.1 Phase I: Experimental Details 9 4.2.2 Hot Tearing Results from Constrained Rod Molds 11 4.2.3 Computer Simulation 14 4.2.4 Instrumented Constrained Rod Mold 18 4.2.5 Phase II: Experimental Details 24 4.2.6 Results and Discussion 24 4.2.7 Summary and Conclusions 30 4.3 TASK 3 Prototype Casting Trials 31 4.3.1 Melting and Casting 31 4.3.2 Results and Discussion 32 4.4 TASK 4 Mechanical Properties and Microstructures 36 4.4.1 Experimental Procedure 36 4.4.2 Results and Discussion 36 4.4.3 Metallography and Microstructure 41 4.4.4 Summary and Conclusions 49 4.5 TASK 5 - Technology Transfer (Casting Trials at Partner Foundry) 50 ii
4.5.1 Phase I: Prototype Castings 50 4.5.2 Melting and Casting 51 3.5.3 Characterization 56 4.5.4 Control of Hot Tearing 59 4.5.5 Summary and Conclusions 59 4.5.2 Phase II: 4.5.2 Mounting Bracket Casting 61 4.5.2.1 Computer Simulation 61 4.5.2.2 Simulation Results 67 4.5.2.3 Summary and Conclusions 74 4.5.2.4 Casting Trials 75 4.5.2.5 Casting Trial Highlights 77 4.5.2.6 Microstructures from Selected Bracket Components 85 4.5.2.7 Summary and Conclusions 91 4.5.3 Characterization (Mechanical Properties) 92 4.5.3.1Test bars 92 4.5.3.2 Results and Discussion 92 4.5.3.3 Summary and Conclusions 100 5 Benefits Assessment 101 6 Commercialization 101 7 Accomplishments 101 7.1 Control of Hot Tearing 101 7.2 Publications 102 8 Conclusions 102 9 Recommendations 104 10 References 104 11 Appendices 106 iii
List of Figures Figure 4.1.1 Restrained rod hot-tearing molds. ..................................................................................................... 6 Figure 4.1.2 Instrumented restrained mold showing the location of thermocouples. ............................................ 7 Figure 4.1.3 Engine mount mold halves. ............................................................................................................... 8 Figure 4.1.4 Rocker arm mold halves and metal core. .......................................................................................... 9 Figure 4.2.1 Typical sectioned RPT samples (a) before, and (b) after degassing. ................................................. 9 Figure 4.2.2 Macrostructures of disc castings (a) before, and (b) after adding grain refiners. ............................ 10 Figure 4.2.3 Photographs of 3-rod constrained casting showing location of hot tearsing. .................................. 12 Figure 4.2.4 Simulation results for alloy 206.0 at 290°C and 450°C. ................................................................. 16 Figure 4.2.5 Comparative hot tearing potential at 290 and 450°C for alloy 206.0. ............................................. 17 Figure 4.2.6 Simulation results for alloy 535.0 at 290 and 450°C. ...................................................................... 18 Figure 4.2.7 Alloy 206.0 showing the effects mold temperatures on hot tearing. ............................................... 20 Figure 4.2.8 Anodized microstructures of 206.0 (a) before and (b) after grain refinement. ................................ 21 Figure 4.2.9 Restrained casting from alloy 535.0 without hot tearing ................................................................. 21 Figure 4.2.10 Cooling curves and its first derivative near the ingate and the rounded end of the 26 cm rod poured from unrefined melts of alloy 206. .................................................................................................................. 22 Figure 4.2.11 Cooling curves and its first derivatives from the top, middle, and the bottom of the sprue poured from unrefined melts of alloy 206. .............................................................................................................................. 22 Figures 4.2.12 Refined metal poured into molds preheated to (a) 300°C and (b) 400°C. ................................... 25 Figure 4.2.13 Examples of cooling curves at the rod/sprue and rod/ball junctions ............................................. 27 for a 10 inch rod at solidus temperature. .............................................................................................................. 27 Figure 4.2.14 Examples of cooling curves at the rod/sprue and rod/ball junctions for a 10 inch rod at solidus temperature from which the cooling rate was estimated. ............................................................................................. 28 Figure 4.3.1 Photographs of engine mount castings without and with hot tear. .................................................. 33 Figure 4.3.2 Radiographs from A206.0 and A535............................................................................................... 33 Figure 4.3.3 Photographs of a mounted rocker arm mold and rocker arm casting. ............................................. 34 Figure 4.3.4 Examples of hot tear and surface shrinkage in rocker arm castings. ............................................... 35 Figure 4.4.1 Effect of Cu content on the tensile properties of alloy 206. ............................................................ 39 Figure 4.4.2 Effect of test temperature on the tensile properties of alloy 206 with 5.1%Cu. .............................. 39 Figure 4.4.3 Effect of Mg content on the tensile properties of alloy 535 ............................................................ 40 Figure 4.4.4 Hot-tear region of constrained rod castings from alloys 206 and 535. ............................................ 41 Figure 4.4.5 Microstructures from alloy 206 poured in mold preheated to 200°C. ............................................. 42 Figure 4.4.6 Microstructures from alloy 206 poured in mold preheated to 350°C. ............................................. 43 Figure 4.4.7 Microstructures from alloy 206 poured in mold preheated to 400°C. ............................................. 44 Figure 4.4.8 Anodized and etched microstructures showing the progression of hot tear. ................................... 44 Figure 4.4.9 Unetched microstructures of test bars of alloy 206 before and after heat treatment. ....................... 45 Figure 4.4.10 Microstructures of test bars of alloy 206 before and after heat treatment. Keller's etch. .............. 45 Figure 4.4.11 Microstructures from test bars of alloy 206................................................................................... 46 before and after heat treatment. Keller's etch. ...................................................................................................... 46 Figure 4.4.12 Alloy 206, SEM of the fracture surface of test bar showing dendritic structure. The EDS of the general area and eutectic area are shown in (e) and (f). ............................................................................................... 47 Figure 4.4.13 Unetched and etched microstructures of test bars of alloy 535 before .......................................... 48 in addition, after heat treatment, 500x. ................................................................................................................. 48 Figure 4.4.14 Alloy 535, SEM of (a) fracture surface, (b) dendritic structure of (a), and (c) EDS. .................... 48 Figure 4.5.1 Mounted 4-cavity swivel mold on tilt-pour machine. ..................................................................... 50 Figure 4.5.2 Schematic of sand core and swing arm casting with gating system and feed tube. ......................... 51 Figure 4.5.3 Mounted swing arm mold on LP machine with T/C and cooling channel probes. .......................... 51 Figure 4.5.4 Photographs of swivel castings with and without the gating system. .............................................. 54 Figure 4.5.5 Radiographs of swivel casting from A206 and A535. No hot tear or shrinkage cavity. ................. 54 Figure 4.5.6 Photographs of elbow casting with and without the gating system ................................................. 55 iv
Figure 4.5.7 Radiographs of elbow casting from A206 and A535. ..................................................................... 55 Figure 4.5.8 Swing arm casting with gating system, sand core, and finished casting. ........................................ 56 Figure 4.5.9 Predicted and observed hot tear location on casting on casting. ..................................................... 56 Figure 4.5.10 Sectioned and macroetched swivel head castings from alloys 206 and 535. ................................. 57 Figure 4.5.11 Anodized microstructures from grain refined swivel-head casting from alloys 206 and 535. Etched with 1.8% fluoboric acid (HBF4) in water (Barkers's anodizing method). ..................................................... 57 Figure 4.5.12 Microstructures from swing arm castings. .................................................................................... 58 Figure 4.5.13 SEM of fracture surface from swing arm casting. ......................................................................... 58 Figure 4.5.14 Bracket component poured from A356 ......................................................................................... 61 Figure 4.5.15 Bracket casting with gating system. .............................................................................................. 62 Figure 4.5.16 Thermocouple locations for the casting trials and simulation. ...................................................... 62 T1 and T2 are locations of thermocouples in the mold. ....................................................................................... 62 Figure 4.5.17 Hot tearing predicted in the cross bracket. .................................................................................... 67 Figure 4.5.18 Casting #12 showing hot tearing location in the upper cross member junctions. .......................... 68 Figure 4.5.19 Casting #10 showing hot tearing in the transition from the post to the journal area. .................... 68 Figure 4.5.20 Minor hot tearing tendencies at the top cross bar. ......................................................................... 69 Figure 4.5.21 Minor secondary shrinkage predicted underneath top risers ......................................................... 69 Figure 4.5.22 Example of mold filling results. .................................................................................................... 70 Figure 4.5.23 Potential areas where contraction stresses can develop and .......................................................... 71 promote mechanical hot tearing are shown by the arrows. ................................................................................... 71 Figure 4.5.24 Areas where minor shrinkage is predicted when die opens ........................................................... 71 Figure 4.5.25 Predicted maximum principal stress and maximum principal strain when die was opened after 120 seconds. ................................................................................................................................................................ 72 Figure 4.5.26 Predicted areas where hot tearing will develop towards the end of solidification ......................... 72 Figure 4.5.27 Minor hot tearing tendencies at the bottom cross bar. ................................................................... 73 Figure 4.5.28 Minor secondary shrinkage predicted underneath un-insulated top riser. ..................................... 73 Figure 4.5.29 Closed mold showing location of the two thermocouples. ............................................................ 75 Figure 4.5.30 Spot where mold surface temperature (IR #3) was measured, near the pouring cup .................... 75 Figure 4.5.31 Spot where mold surface temperature (IR #4) was measured, ...................................................... 76 flange under the hoop section. .............................................................................................................................. 76 Figure 4.5.32 Photograph of casting with gating system. .................................................................................... 78 Figure 4.5.33 Photograph of finished component. ............................................................................................... 78 Figure 4.5.34 Examples of X-ray radiographs showing area where surface shrinkage was observed. ................ 79 Figure 4.5.35 Mold and pouring temperatures from melt A206-1. ...................................................................... 83 Figure 4.5.36 Mold and pouring temperatures from melt A206-2. ...................................................................... 83 Figure 4.5.37 Mold and pouring temperatures from melt B206. ......................................................................... 84 Figure 4.5.38 Mold and pouring temperatures from melt 535. ............................................................................ 84 Figure 4.5.39 A sectioned casting showing locations A and B ............................................................................ 85 where samples for microstructure evaluation were removed................................................................................ 85 Figure 4.5.40 Unetched as-cast microstructures from component #35 alloy A206. ............................................ 85 Figure 4.5.41 Unetched as-cast microstructures from component #64 alloy 535. ............................................... 86 Figure 4.5.42 As-cast microstructures from component #35 alloy A206. ........................................................... 87 Figure 4.5.43 As-cast microstructures from component #44 alloy B206. ........................................................... 87 Figure 4.5.44 Heat treated microstructures from component #51 alloy B206 ..................................................... 88 Figure 4.5.45 As-cast microstructures from component #64 alloy 535. .............................................................. 88 Figure 4.5.46 Photograph of fracture surface from casting #10 alloy A206, 1.2x. .............................................. 89 Figure 4.5.47 SEM photographs of fracture surface from casting #10 of A206. ................................................. 89 Figure 4.5.48 Unetched microstructures from casting #10 perpendicular to the fracture surface. ...................... 90 Figure 4.5.49 Etched microstructures from broken casting #10. ......................................................................... 90 Figure 4.5.50 Bracket casting showing areas where test bars were removed. ..................................................... 93 Figure 4.5.51 Photographs of machined and separately cast test bars. ................................................................ 93 Figure 4.5.52 (a) Tensile properties and (b) elongation from as-cast and after heat treatment. ........................... 94 Figure 4.5.53 Microstructures from test bars poured from B206 in as-cast and .................................................. 95 after heat treatment. Keller's etch, 500x. .............................................................................................................. 95 Figure 4.5.54 Mechanical properties of test bars machined from bracket casting of A206-1. ............................ 97 Figure 4.5.55 Mechanical properties of test bars machined from bracket casting of A206-2 ............................. 97 v
Figure 4.5.56 Mechanical properties of test bars machined from bracket casting of B206. ................................ 98 Figure 4.5.57 Mechanical properties of separately cast test bars of A206........................................................... 98 Figure 4.5.58 Microstructures from test bars machined from the bracket component in vertical (17-1) and horizontal (17-2) orientation. Etchant is Keller's reagent. ........................................................................................... 99 Figure 4.5.59 SEM of fracture surface of tensile bars in vertical (17-1) and horizontal (17-2) orientation. Dendritic structure and shrinkage voids are shown. .................................................................................................. 100 List of Tables Table 4.2.1 Processing parameters for computer simulation ............................................................................... 11 Table 4.2.2 Chemical analysis of alloy 206 for hot tearing studies ..................................................................... 11 Table 4.2.3 Chemical analysis of alloy 535 for hot tearing studies ..................................................................... 11 Table 4.2.4 Processing parameters of alloy 206 melt # N6080 ............................................................................ 13 Table 4.2.5 Processing parameters of alloy 206 melt # N6081 ............................................................................ 13 Table 4.2.6 Processing parameters of alloy 206.0 melt # N6090 ......................................................................... 14 Table 4.2.7 Processing parameters of alloy 535.0 melt # N6082 ......................................................................... 14 Table 4.2.8 Summary of the simulation results of the restrained rod castings ..................................................... 15 Table 4.2.9 Processing parameters of alloy 206 melt # N7057 ............................................................................ 19 Table 4.2.10 Processing parameters of alloy 206 melt # N7072 .......................................................................... 19 Table 4.2.11 Processing parameters of alloy 206 melt # N7073 .......................................................................... 19 Table 4.2.12 Processing parameters of alloy 535 melt # N7074 .......................................................................... 20 Table 4.2.13 Chemical analysis of alloy 206 ....................................................................................................... 24 Table 4.2.14 Effects of mold temperature and grain refiner addition on hot tearing ........................................... 26 Table 4.2.15 Estimated cooling rate from melt N2051A-4 mold preheated to 200°C ......................................... 29 Table 4.2.16 Estimated cooling rates from melt N2052A-4 mold preheated to 350°C ....................................... 29 Table 4.2.17 Estimated cooling rates from melt N2054A-4 mold preheated to 400°C ....................................... 29 Table 4.3.1 Chemical analysis of A535 ............................................................................................................... 31 Table 4.3.2 Chemical analysis of A/B206 ........................................................................................................... 32 Table 4.3.3 Processing parameters for engine bracket castings ........................................................................... 33 Table 4.3.4 Processing parameters of the rocker arm castings ............................................................................ 34 Table 4.4.1 Chemical analysis of alloy 206 ......................................................................................................... 37 Table 4.4.2 Chemical analysis of alloy 535 ......................................................................................................... 37 Table 4.4.3 Mechanical properties of alloy 206 in the F, T4 and T7 tempers ..................................................... 38 Table 4.4.4 Effect of test temperature on properties of alloy 206.0, melt N6090 ................................................ 39 Table 4.4.5 Mechanical Properties of alloy 535 in the F and T5 tempers ............................................................ 40 Table 4.5.1 Chemical analysis of A535 ............................................................................................................... 53 Table 4.5.2 Chemical analysis of A/B206 ........................................................................................................... 53 Table 4.5.3 Processing temperatures for swivel castings ..................................................................................... 53 Table 4.5.4 Processing parameters for A356 ....................................................................................................... 63 Table 4.5.5 Processing parameters for A206 ....................................................................................................... 64 Table 4.5.6 Summary of iterations and die cycle for A206 ................................................................................. 65 Table 4.5.7 Processing parameters for 535 .......................................................................................................... 66 Table 4.5.8 Summary of iterations and die cycle for 535 .................................................................................... 66 Table 4.5.9 Chemical analysis of alloy A206 ...................................................................................................... 77 Table 4.5.10 Chemical analysis of alloy B206 .................................................................................................... 77 Table 4.5.11 Chemical analysis of alloy 535 ....................................................................................................... 77 Table 4.5.12 Processing temperatures from thermocouples ................................................................................ 81 and infrared pyrometer for A206-1 ...................................................................................................................... 81 Table 4.5.13 Processing temperatures from thermocouples ................................................................................ 81 and infrared pyrometer for A206-2 ...................................................................................................................... 81 Table 4.5.14 Processing temperatures from thermocouples ................................................................................ 82 and infrared pyrometer for alloy B206 ................................................................................................................. 82 vi
Table 4.5.15 Processing temperatures from thermocouples ................................................................................ 82 and infrared pyrometer for alloy 535 .................................................................................................................... 82 Table 4.5.16 Chemical analysis of alloy 206 ....................................................................................................... 94 Table 4.5.17 Average Properties and standard deviation from ASTM B108 test bar of alloy 206 ...................... 94 Table 4.5.18 Chemical analysis of alloy A/B206 ................................................................................................ 96 Table 4.5.19 Chemical analysis of alloy 535 ....................................................................................................... 96 Table 4.5.20 Average properties from bars machined from component .............................................................. 97 vii
1 Executive Summary The current federal regulations on the fuel economy and emissions make it imperative that the current vehicles need to be more fuel efficient. The fuel efficiency can be improved in many ways, including power train modifications, electrification, and light weighting of the vehicle. Usually automotive manufacturers incorporate a combination of these technologies. Every 10% reduction in weight can improve the fuel efficiency by 6% and reduce GHG emissions by 3%. Current vehicles use mostly ferrous components for structural applications. It is possible to reduce the weight of the vehicle by substituting these parts with those made from light metals such as aluminum and magnesium. Many alloys and manufacturing processes can be used to produce these light metal components and casting is known to be most economical. One of the high integrity casting processes is permanent mold casting which is the focus of this research report. Many aluminum alloy castings are used in automotive applications and the majority of them are produced by the sand casting process. Also, aluminum-silicon (Al-Si) alloys are the most widely used alloy systems for automotive applications. It is possible that by using high strength aluminum alloys based on an aluminum-copper (Al-Cu) system and permanent mold casting, the performance of these components can be enhanced significantly. This will also help to further reduce the weight. However, many technological obstacles need to be overcome before using these alloys in automotive applications in an economical way. There is very limited information in the open literature on gravity and low-pressure permanent mold casting of high strength aluminium alloys. This report summarizes the results and issues encountered during the casting trials of high strength aluminum alloy 206.0 (Al-Cu alloy) and moderate strength alloy 535.0 (Al-Mg alloy). Five engineering components were cast by gravity tilt-pour or low pressure permanent mold casting processes at CanmetMATERIALS (CMAT) and two production foundries. The results of the casting trials show that high integrity engineering components can be produced successfully from both alloys if specific processing parameters are used. It was shown that a combination of melt processing and mold temperature is necessary for the elimination of hot tears in both alloys. A focused study, using constrained rod castings in metal molds on the effects of grain refinement and mold temperature on the hot tearing resistance of both alloys, exhibited that the combination of grain refinement and mold temperatures had resulted in lower strain rates which was proven to be necessary to prevent the formation of hot tearing during the solidification. The associated simulation efforts indicated that the constrained rod castings poured in metal molds at lower temperatures (around 290˚C) develop higher maximum principal strain rates during the last stages of solidification as compared to those cast in molds held at more than 400°C. This trend was similar to both alloys and simulation results closely match the hot cracking trends observed experimentally. The reduced hot cracking in the hotter mold is attributed to the reduced principal strain during the last stages of solidification. The report also presents the results from the evaluation of mechanical properties, in both as-cast and heat- treated conditions using separately cast ASTM B108 tensile bars. It was also shown that the mechanical properties of the castings produced met or exceeded the required aerospace standards. The results from this work should make it easier for automotive designers to confidently use the high strength aluminum alloys in vehicles. 1
2 Introduction Weight reduction of vehicles is one of the major efforts being undertaken by automakers worldwide in their increased emphasis to improve fuel economy. The use of aluminum and magnesium alloys as replacements for the existing ferrous components is one strategy to reduce the weight of vehicles. These light metal components can be produced through many high integrity manufacturing processes such as gravity and low pressure permanent mold casting. Some of the advantages of permanent mold casting process compared to sand casting processes are better surface finish, precise and consistent dimensional control and improved mechanical properties. A number of foundries currently produce aluminium components for the automotive, electrical, marine and agricultural sectors by gravity tilt-pour and low pressure permanent mold casting processes. A majority of these castings are produced from aluminium-silicon family alloys, namely 356.0 (Al-Si) and 319.0 (Al-Si-Cu). These alloys, despite being easy to cast, do not possess very high strengths and have only moderate toughness. Other high strength aluminum alloys based on the Al-Cu system can reduce the weight further as compared to Al-Si alloys. The high strength Al-Cu alloy 206 is usually produced by sand casting for aerospace applications. Similarly Al-Mg alloy 535 has a good combination of strength and ductility, shock resistance, and dimensional stability in the as-cast condition and is used in automotive, marine and military applications. Both of these alloys are prone to hot tearing (hot shortness) when poured in permanent molds due to their long freezing ranges. There is limited information in the literature on the gravity and low-pressure permanent mold casting of high strength aluminium alloys 206 and 535. The use of magnesium for automotive applications is gaining momentum as increased weight savings is being targeted. There are several ongoing research efforts on the development of new creep resistance magnesium alloys that have improved high temperature properties for automotive applications. It is anticipated that some automakers may increase their use of magnesium from the 4 kg per vehicle in 2005 to about 100 kg by 2020. Currently, the major production route of magnesium alloy components used in automotive applications is by high-pressure die-casting. However, due to porosity, most of the high pressure die cast components cannot be heat-treated. Gravity tilt-pour, and low-pressure permanent mold casting of powertrain components from magnesium alloys can lead to reduced porosity defects, and thus allow for the heat treatment of the prototype components for improved performance. The use of magnesium in other applications is also expected to increase due to its high-strength-to-weight-ratio. Therefore the selection of alloys 206 and 535 and some magnesium alloys for more rigorous engineering applications is currently hampered by lack of adequate data on the foundry characteristics and the mechanical properties in metal permanent molds. This research was initiated to address some of the issues identified above. 2
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