Mechanical behavior of A356 matrix nanocomposites fabricated using two step mixing via stir casting technique
In this work an investigation of compressive strength and forgeability behavior have been made to explore the effect of SiC nano particles on A356 alloy matrix for the development of A356/SiC nanocomposites using two step mixing through stir casting technique. A356 alloy ingot was selected as a matrix and AFP+SiCn (99.9% pure aluminium fine powder+nano size SiC mechanically forged by using ball mill at 100 rpm for duration of 10 hours) as a reinforcement. Argon gas was used to protect from oxidation during ball milling process. SiC nano particles were varied from 1% to 5% in a step of 1% by weight. In stir casting technique, stirring process was performed at 500±50 rpm for mixing AFP+SiCn in the melt matrix for total stirring period of 10 minutes in two steps. Composites were poured at 680±20° C into the permanent mould. Compressive strength and forgeability tests of fabricated nanocomposites were evaluated by using hydraulic pellet press machine. To analyze the fractured mechanism SEM microstructure was examined. The presence of SiC nano particles were confirmed by EDX spectrum. It was revealed from the results that compressive strength increases with increment of SiC nano particles and found as 603 MPa at 5% SiC nano particles. Whereas forgeability of the nanocomposites were decreased with the increment of SiC nano particles. SEM micrographs showed the ductile fractured mechanism was dominant over the brittle fracture. The main constituents present in the nanocomposites were verified by EDX spectrum.
IMPACT OF STRONTIUM, MAGNESIUM AND NICKEL ON MECHANICAL PROPERTIES OF Al-5 Si-3 Cu (A319) ALUMINIUM ALLOY
1Workshop Instructor, Sreerama Govt. Polytechnic College, Thriprayar, Thrissur 2Professor, Dean, Faculty of Engineering CUSAT, Kerala, India ---------------------------------------------------------------------***--------------------------------------------------------------------Abstract Aluminium and its alloys have number of applications, mainly, in the field of aerospace and automobile industry. A319 (Al-Si) based alloys are used in cylinder heads, engine blocks, suspension etc. The major drawback for this alloy is that of low tensile strength (180 220MPa). Porosity also is a major problem in high pressure and gravity die casting process used for the manufacturing of components. In the present work the major aim is to study the effects of alloying elements Strontium, Magnesium and Nickel in the mechanical properties ofA319. Development of porous free castings using Stir casting technique is also an objective of this work. Six castings were developed for this study (A319, A319 – 0.04Sr, A319 0.05 Ni, A319 –0.5Mg 0.04Sr and A319 – 0.5Mg – 0.5Ni – 0.04Sr). The microstructure and EDAX analysis were done to identify the phases present. Different mechanical tests were carried out to study the effect of these alloying elements on basic A319 alloy. The results showed that these alloying elements have a positive influence on A319 alloy. It is seen that the tensile strength of the material has improved for each alloy composition and maximum tensile strength is obtained as238 MPa for A319 – 0.5Mg –0.5Ni – 0.04Sr alloy.
STRENGTHENING OF COMPOSITES DUE TO MICROSTRUCTURAL CHANGES IN THE MATRIX
Abstract The addition of discontinuous silicon carbide (SiC) to aluminum (Al) alloys can result in a five-fold increase in the yield stress. The magnitude of the increase is obviously a function of the volume fraction and the particle size of the SiC. Previously, it was proposed that the strength increase due to SiC addition to Al alloys was the result of change in the matrix strength, i.e. an increase in dislocation density and a reduction of subgrain size. The data obtained from a series of experiments indicate that dislocation density increases with an increase in volume fraction of SiC and decreases with an increase in particle size. The subgrain size decreases as the volume fraction increases and increases as the particle size increases. There is a good correlation between the microstructural changes in the matrix and the changes in the yield stress of the composites.