Study On Si Phase In Microstructure Of Aluminum Alloy Wheel Hub And Its Raw Materials Under Different Remelting Conditions

A356.2 alloy as the first choice for cast aluminum alloy wheels has become one of the most widely used cast aluminum alloy.How to promote recycling of aluminum alloy wheels is one of the hot topics in the current environment of building a sustainable society.In view of the obvious decrease in the quality and performance of ingots after remelting,the evolution of the microstructural morphology of wasted wheels before and after remelting needs to be systematically studied.In this paper,two materials of the wasted wheels and its the main raw materials are studied,and the changes of aluminum alloy microstructure before and after remelting of these two materials are observed by controlling the overheating temperature and holding time during remelting,focusing on the change of the appearance features,dimensions and content of Silicon phase in the aluminum substrate before and after remelting.The main results obtained by systematic research are as follows:(1)With the increase of the overheating temperature(from 700 ? to 900 ?)and the extension of the insulation time(from 0 h to 2 h),the shape of the silicon phase after the remelting of the aluminum alloy wheels and their raw materials are developed from the dot to the long strip,while the silicon phase area first rises and then falls,the silicon content in the aluminum substrate has been rising.After the hub is remelted,the average length of silicon particles increases from 15.2 ?m to 60.1 ?m with the increase of overheating temperature,the area ratio of silicon phase reaches its maximum when the temperature reaches 800 ?,and the silicon content in the aluminum substation increases from 0.77 % to 1.03 %.The average length of silicon phase particles increases from 7.8 ?m to 21.9 ?m after the wheels are remelted with the increase of holding time,the area of silicon phase reaches a maximum when the holding time is 1.5 hours,and the silicon content in the aluminum substrate increases from 1.0 % to 1.65 %.(2)At the same overheating temperature and holding time,compared with the aluminum alloy wheels with their raw materials,the change regulations are basically the same,but there are differences in values.As the overheating temperature increases,the aluminum alloy wheels are more uniform and small than the raw material in terms of silicon morphology(at least 2 ?m smaller on average in length).The raw material is slightly higher than the length of the alloy wheel in silicon phase and the area of silicon phase is larger(about 5 % higher on average),but the aluminum alloy wheel is higher than the raw material in the silicon content of aluminum substrate.As the holding time increases,the silicon morphology of the hub changes faster and more cluttered than the raw material,and the aluminum alloy wheels are more uniform and smaller than the raw material(at least 5 ?m in length on average).The raw material is slightly higher than the length of the aluminum alloy wheels in silicon phase and its area is larger(by about 2 % on average),but in aluminum substrate silicon content,aluminum alloy wheels are higher than raw materials.The main reasons for the laws of silicon phase evolution in the above results is that with the change of overheating temperature or insulation time,the tiny particles of silicon phase dissolve in the aluminum liquid,resulting in the gradual destruction of the genetic factors of silicon phase,therefore,the morphology of eutectic silicon phase evolves from dot to needle,and the content of silicon in aluminum substrate increases.