Effect Of Rare Earth Modification On Microstructure And Friction Properties Of Al-8Cr-Si Alloy

The rapid development of the national economy has contributed to the rapid development of science and technology.The performance of traditional metal structural materials has been difficult to meet the needs of current industrial products.Therefore,there is an urgent need to improve the strength,plasticity,light weight,corrosion resistance and wear resistance of materials.As one of the widely used light alloys,aluminum alloy is more and more favored by scientific researchers and social needs.Friction and wear is the main form of material failure.According to incomplete statistics,about 70%?80%of equipment damage and 30%?50%of energy consumption are caused by various forms of wear and tear in China every year.Al-Cr alloys have been studied by many scholars because of their excellent wear resistance.Therefore,this article adds alloying element silicon and rare earth cerium to the typical aluminum alloy wear-resistant structural material Al-8%Cr,changing the alloy cooling rate,and studying the effect of cooling rate,alloying element silicon and rare earth cerium on the structure and wear resistance of the material laws,to explore the effect of cooling rate on the alloying effect of alloying element silicon and rare earth cerium,aiming to open up effective ways to improve the structure of metal structures,increase wear resistance and fatigue life.In this experiment,it is attempted to add Si element to Al-8%Cr alloy to obtain excellent wear-resisting Al-Cr-Si phase.Combined with rare earth modification and different cooling rate treatment,the coarse phase in the alloy is further refined and the wear resistance of the alloy is improved.Through the experiment of controlling the alloy cooling rate,the results show that rapid cooling can significantly improve the structure of Al-8%Cr alloy,and its wear resistance and hardness are significantly better than that of conventional cast Al-8%Cr as-cast structure.When cooling at low speed,The as-cast microstructure presents needle-like rod-like Al₁₃Cr₂,and ellipsoid-like Al₁₃Cr₂during high-speed cooling,and its microhardness increases from 65 HV to 83 HV.In the experiment of adding alloy element silicon and rare earth cerium,when the addition amount of alloy element Si gradually increases from 2%to 5%,the second phase changes from a long rod shape to a hollow block shape and then to a long rod shape.The addition of 4%Si makes the precipitated phase Al₁₃Cr₄Si₄appear hollow and massive,and Al₁₃Cr₄Si₄can hinder the growth of long rod-shaped Al₁₃Cr₂,and the precipitated phases are all massive under the condition of rapid cooling.When the addition of rare earth element Ce gradually increases from 1%to 4%,the size of the second phase slowly decreases and then slowly increases.When the additive amount is 2%,the morphology of the aluminum-chromium phase is best improved.When Ce is added,a massive Al₂₀Cr₂Ce will appear,and the precipitated phases are all massive under the condition of rapid cooling.The addition of Si and Ce has a decisive effect on the structure,hardness,wear amount and wear mechanism of the material.The microstructure of Al-8%Cr-4%Si-2%Ce under rapid cooling conditions is more fine and uniform,and its microscopic hardness is about 185 HV at the highest.According to the density functional theory,the influence of the alloying element Si on the formation process of the Al-Cr phase is calculated using the first-principles method.The Al₁₃Cr₄Si₄space group is F-43m,in which covalent bonds and ionic bonds exist at the same time.The calculated Young's modulus of Al₁₃Cr₄Si₄is 180 HV.The calculation results show that the second phase with high hardness is a potential excellent wear-resistant phase.Comparative wear resistance experiments show that the average friction coefficient of Al-8%Cr alloy is 1.23;the average friction coefficient of Al-8%Cr-4%Si is 1.19;the average friction coefficient of Al-8%Cr-2%Ce it is 1.20;the average friction coefficient of Al-8%Cr-4%Si-2%Ce is 1.18.Observing the wear surface morphology of the alloy,there are Al-8%Cr-4%Si-2%Ce alloys with higher hardness,Al₁₃Cr₂,Al₁₃Cr₄Si₄,Al₂₀Cr₂Ce,with shallow furrows and relatively flat wear surfaces.Therefore,the higher the hardness of the second phase in the alloy,the better the wear resistance of the Al-8%Cr alloy.