Effect Of Rare Earth Y On Microstructure And Properties Of A356 Alloy

A356 alloy is the most commonly used in the aluminum alloy family, and it not only has good casting performance and mechanical processing performance, but also has the advantages of good fluidity, air tightness, shrinkage and thermal cracking tendency. At present, it’s widely used in the automotive, aerospace and other manufacturing industries. However, in the conventional as-cast condition, the microstructures of A356 alloy consist of coarse α-Al dendrites and eutectic Si, and eutectic Si randomly distributed along dendrites is in thick plate strip or needle. It seriously divided the matrix and reduces the strength and ductility of the alloy. Therefore, that how to change the morphology of α-Al grains, and the size and distribution of eutectic Si has become the key to improve the mechanical properties of the A356 alloy.Firstly, by adding different content of rare earth yttrium into the A356 alloy, the effect of yttrium on the as-cast microstructures and properties of A356 alloy is studied. Secondly, the impact of T6 heat treatment process and T6I6 two-stage process on microstructures and mechanical properties is studied. Finally, using the research results and numerical simulation technology design the gating system of roller bearing and it effectively solve the problem of the poor strength and low plasticity of roller bearing for the enterprise.The results show that rare earth yttrium not only can refine the α-Al grains and reduce the dendrite arm spacing, but also improve the morphology of eutectic Si from the bar-like or needle-like to acicular or short rod. Meanwhile, rare earth yttrium has the inhibitory effect on the stomata of the A356 alloy. When the rare earth yttrium content is 0.3%, the alloy organization has been significantly improved, and its mechanical properties have the initial upgrade.A356 alloy belongs to the heat-strengthened alloy, and the heat treatment can greatly improve the performance of the alloy. In order to continue to enhance the mechanical properties of rare earth A356 alloy, the effects of T6 heat treatment process parameters on microstructures and properties of the alloy is studied, and it is concluded that T6 heat treatment optimized process is 535℃×4.5h + 145℃×4h. At the same time, we study the effect of T6I6 two-stage process on microstructures and properties of A356 alloy and optimize the T6I6 two-stage process parameters. When the pre-aging is 120℃×3h and the re-aging is 180℃×1h, the spherical degree and uniformity of Si particles is superb, and the tensile strength of the alloy can reach 289 MPa, and the elongation is at around 10%~11%, and the hardness is 91.Using the research results and combining with the numerical simulation technology, we have verified the problem of enterprise. Based on numerical simulation Pro CAST software, we carried out numerical simulation for roller bearing to predict the location and area of the defect, and optimized the casting process parameters and set the reasonable feeders and chills to obtain the feasible gating system and to produce the complete roller bearing casting. After the modification of rare earth yttrium and the T6I6 two-stage aging process, the load of roller bearing can reach 2500 kg, therefore, it solves the enterprise’s practical problems.