Investigation On Microstructure And Properties Of A356Alloy Wheel For Low Pressure Die

In this paper, A356alloy wheel of low pressure die casting is investigated.using oftesting some methods such as, Differential Scanning Calorimetry (DSC), ScanningElectron Microscope (SEM), and X-ray diffraction (XRD) etc, which were used toexamine the influences of microstructures and mechanical properties of Al-10Sr, Al-Ti-Band Al-Ti-C. The main research results are as follow:Modification by Al-10Sr alloys of eutectic silicon in the A356alloy microstructurewas sufficient. In the wheel castings the content of Sr was good from0.005to0.008percent. Grain refinement of Al-Ti-B or Al-Ti-C refined dendrite spacing and dendritespacing was below100μm. The results of T6heat treatment showed that the eutecticsilicon phase of the A356alloy under1h solution treatment was changed a little, most ofwhich were long strip shape and sharp angled. Eutectic silicon phase under the solutiontreatment at6h was granular or spherical distribution, roundness and uniformity ofgranulation silicon crystal was also good, and particle of Si crystal was smaller. Theeutectic silicon phase under the solution treatment at11h was coarsened, whoseroundness and uniformity were also poor.The mechanical properties of A356alloy of modification and grain refinement by lowpressure die casting was that elongation was4%, below specification and tensile strengthwas220Mpa above specification. The fracture morphology of tensile specimens isanalysed by SEM. The morphology is ductile fracture with shallow dimples. Aftersolution treatment for535℃×4-6h and aging treatment is for145℃×4h. Themicro-appearance is plastic fracture, and the dimples become deep and equiaxed. After T6compared with A356alloy refined by Al-Ti-C and refined by Al-Ti-B the mechanicalproperties as follows, the former to the latter, elongation is above15%, yield strength isabove8%and tensile strength is above8%. Then by Paint baking treatment, both of themtensile strength increased by10%yield strength increased by20%, but elongation reduced10%.compared with T6treatment and Paint baking treatment, the ratio of yield strengthand tensile strength increased from0.6-0.7to0.7-0.8. The temperature range of solids-liquids states was obtained through DSC curve of A356alloy. It’s about567.8℃-630.2℃. The liquidus temperature was616.3℃and the eutecticstarting temperature was572.1℃. As the undercooling increases,so the nucleation rateincreases. The growth of silicon phase was inhibited, and became slow. Its modificationeffect was excellent. The aging phase precipitation of a356alloy in low temperature isdiscussed by DSC. G.P zone is precipitated from60to70℃, because of the clusters ofvacancys, nor the diffusion of Si and Mg elements in G.P zone. β``and β`phase areformed when the temperature is150℃or so,because of the diffusion of Si and Mgelements and the pinning dislocation in G.P zone. The properties of A356alloy willbecome good. When the heating temperature is beyond250℃, the equilibrium phase of βphase is precipitated from the matrix of A356alloy.