Evaluation of the mechanical properties of friction stir lap welded joints for dissimilar aluminum alloys(AA1100 To AA6061)
In this study friction stir lap welding (FSLW) joints are made for similar and dissimilar aluminum alloys (AA1100 to AA6061-T6) sheets of 3mm thickness by varying the welding parameters, such as tool rotation speeds (1000, 1250 & 1600 rpm) and welding speeds (35, 75 & 100 mm/min) and pin length of (2.8, 5.4 & 5.7mm) with using cylindrical threaded tool pin profile. Many tests and inspections were performed such as X-Ray radiographic and tensile shear test to evaluate the weld quality and joint efficiency under different welding parameters. Microhardness and microstructure observations were carried out at the best welding parameters. The maximum tensile shear force (4.93 KN) and joint efficiency (93%) were obtained when welding process was conducted by a new technique with using friction stir diffusion welding process at the welding speed of 75 mm/min, tool rotation speed of 1250 rpm and using pin length of 2.8 mm. It was found that the Vickers hardness of the similar and dissimilar joints reached to the maximum value at stir zone and drop toward the base metals.
Unified Principal S–N Equation for Friction Stir Welding of 5083 and 6061 Aluminum Alloys
With the popularization of friction stir welding (FSW), 5083-H321 and 6061-T6 aluminum alloy materials are widely used during the FSW process. In this study, the fatigue life of friction stir welding with two materials, i.e., 5083-H321 and 6061-T6 aluminum alloy, are studied. Fatigue tests were carried out on the base metal of these two materials as well as on the butt joints and overlapping FSW samples. The principle of the equivalent structural stress method is used to analyze the FSW test data of these two materials. The fatigue resistances of these two materials were compared and a unified principal S–N curve equation was fitted. Two key parameters of the unified principal S–N curve obtained by fitting, C d is 4222.5, and h is 0.2693. A new method for an FSW fatigue life assessment was developed in this study and can be used to calculate the fatigue life of different welding forms with a single S–N curve. Two main fatigue tests of bending and tension were used to verify the unified principal S–N curve equation. The results show that the fatigue life calculated by the unified mean 50% master S–N curve parameters are the closest to the fatigue test results. The reliability, practicability, and generality of the master S–N curve fitting parameters were verified using the test data. The unified principal S–N curve acquired in this study can not only be used in aluminum alloy materials but can also be applied to other materials.
Failure analysis for poor solderability of Au surface of PCB
Nonwetting is one of the common problems and is always rejected in electronic assemblies. ENIG pads of a PCBA exhibited nonwetting after lead-free reflow soldering. With the aid of stereomicroscope, SEM&EDS and XRF, a series of analysis was performed. And after visual inspection, surface and cross section analysis, thickness measurement and solderability test, it can be inferred that oxidation of plating surface was the main reason for nonwetting, and corrosion in Ni plating caused an adverse impact on solderalibity.