Effect of Different Solution Treatments on Microstructure and Properties of Hypoeutectic Al-Si Alloys
In the as-cast hypoeutectic Al-Si alloy,the coarse a-Al grains and needle-like eutectic Si are the main reasons for its reduced performance.In this study,the Al-7Si alloy refined by Al-Ti-La and Nd was subjected to different conditions of solution treatment to investigate the influence of different solution temperatures and times on its microstructure and properties.The results show that with the increase of solution temperature,the secondary dendrite arm spacing(SDAS)of the as-cast Al-7Si alloy gradually increases,while the size of eutectic Si decreases,and the eutectic Si transforms from a long strip-like and fibrous shape to a short rod-like shape.With the prolongation of solution time,the evolution process of eutectic Si changes from long strip-like to short rod-like,then to granular,and finally to coarsening and growth.When the solution temperature is 535 ℃ and the solution time is three hours,the alloy's microhardness is 62.5 HV,which is 10.5％higher than that of the as-cast state.The ultimate tensile strength(UTS)and elongation(El)increase from 170.2 MPa and 11.1％in the as-cast state to 174.0 MPa and 13.1％,respectively,representing 2.2％and 18.0％improvement.The fracture surface exhibits a small cleavage plane and a large area of ductile dimples,indicating a transition from brittle fracture to ductile fracture.
Al-7Si alloysolid solution treatmentSADSeutectic Si
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