Effects Of Different Modifiers On Creep Properties Of Aluminum Alloy Hub Materials And Their Applications

In the situation of energy crisis and environmental problems in modern society,reducing the weight of the vehicle to promote the lightening of the vehicle is an effective means to improve the fuel efficiency of the vehicle,save energy and reduce exhaust emissions.Therefore,cars in today’s society are more inclined to choose light weight,excellent comprehensive performance,good surface quality,recyclable and low-cost materials for production.A356aluminum alloy precisely composite above characteristics.A356 aluminum alloy has many excellent characteristics,such as good fluidity in the molten state.After solidification,the air tightness of alloy castings is small,but coarse primaryα-Al phase dendrites and long acicular eutectic silicon can be observed in the microstructure of conventional as-cast A356 aluminum alloy.The long acicular eutectic silicon is prone to stress concentration at its tip.It is easy to destroy the matrix structure and reduce the properties of the alloy.Therefore,in the process of industrial production,metamorphic treatment is usually used to improve the microstructure and properties of alloy.In this paper,Al-10Sr modifier,new modifier and La-Ce mixed rare earth modifier were selected to respectively modify A356 aluminum alloy.Through X-ray diffraction（XRD）,microstructure analysis（OM）,scanning electron microscopy（SEM）and tensile properties test,the modification effects of different modifiers on the microstructure of A356 aluminum alloy were analyzed.The effects of three modifiers on the eutectic silicon morphology of A356aluminum alloy were studied.After T6 heat treatment,the alloy castings were placed at 150℃and the creep experiment was carried out under the stress of 200MPa to study the effects of different modifiers on the creep properties of A356 aluminum alloy.At the same time,the effects of cooling rate on the morphology of eutectic Si of A356 aluminum alloy and Al-10Sr and the new type of modifier were studied,and the alloy was treated with T6 to study the morphology and tensile properties of eutectic Si after heat treatment.（1）The study of A356 aluminum alloy with different modifiers found that with the addition of modifiers,the eutectic silicon size of A356 aluminum alloy was reduced and the properties were greatly improved.By comparing the microstructure of A356 aluminum alloy with different modifier,the new modifier has the best effect on the microstructure of A356aluminum alloy.By adjusting the content of the new modifier in A356 aluminum alloy,it was found that the modification effect first increased and then decreased with the increase of the content of the new modifier.When the content of the new modifier was 0.6%,the modification effect was the best.The size of the eutectic silicon was smaller,and the average length of the eutectic silicon was 1.56μm and the average width was 0.72μm.Eutectic silicon roundness is2.17.（2）The effects of different cooling rates on the A356 aluminum alloy with the addition of Al-10Sr modifier and the new modifier are studied.It is found that the Al-10Sr modifier and the new modifier are particularly sensitive to the cooling rate of the alloy.The size of the eutectic silicon decreases with the increase of the cooling rate,and the secondary dendrite spacing of the primaryα-Al phase decreases obviously.The length of long acicular eutectic silicon becomes smaller and the number of branches increases.When the cooling rate is 45℃/s,the eutectic Si size of Al-10Sr modifier and the new modifier is the smallest,the average length is 2.75μm and1.37μm,and the roundness is 3.77 and 2.85,respectively.At the same time,after T6 heat treatment,it is found that the eutectic silicon size of the alloy decreases gradually with the increase of cooling rate,and the tensile property of A356 aluminum alloy castings is greatly improved.At the cooling rate of 45℃/s,the eutectic Si size of T6 A356 aluminum alloy with Al-10Sr modifier and the new modifier is the smallest,with the average length of 3.35μm and2.83μm,the circularity of 1.81 and 1.45,and the tensile strength of the alloy are 250MPa and278MPa,respectively.It is found that at the same cooling rate,the new type of modifier has better metamorphic effect on A356 aluminum alloy.（3）The creep properties of T6 A356 aluminum alloy were investigated by adding different modifier.It was found that the creep properties and creep life of A356 aluminum alloy were improved obviously after adding modifier.Among them,A356 aluminum alloy with 0.6%new modifier has the best creep resistance,and the steady state creep rate is 5.63×10^-6s^-1,which is 99.62%lower than that of the matrix alloy.