| Al-7Si-0.4Mg(wt.%)casting alloys can be extensively applied in a large number of components in the automotive and aeronautical industries,owing to their excellent castability,high strength/weight ratio and good corrosion resistance.The process of lightweighting puts forward new requirements for the performance of automotive structural parts.The main problem in the application of cast aluminum alloy materials is that they are not high in strength and toughness,which limits their wider application in automotive components.Microalloying is one of the main methods to improve the properties of cast Al alloys.Many studies have shown that Al3M-type intermetallics can effectively improve the properties of cast aluminum alloys.Generally,the transition metal elements that can form Al3M-type intermetallics in aluminum alloys include Sc,Y,Ti,Zr,and Hf,among which Zr and Ti are relatively low cost.Therefore,this paper proposes to strengthen the traditional Al Si7Mg0.4 casting alloy with a proper amount of Zr and Ti element microalloys.The effect of Zr on the microstructure and mechanical properties of AlSiMg alloys and the effect of refiners on the microstructure and mechanical properties of AlSiMg Zr alloys are studied.At the same time,the aluminum alloy wheel was trial-produced using the alloy with the best performance.In this paper,phase diagrams and solidification processes of as-cast alloys were calculated by the Thermo-Calc and the JMat Pro software.Based on this,four Al-7Si-0.4Mg-x Zr alloys with different Zr content are prepared by gravity casting(where x=0,0.06%,0.14%,0.20%),and analyzed the effects of different contents of Zr on the microstructure,mechanical properties and fracture morphology of the as-cast and heat-treated Al-7Si-0.4Mg-x Zr alloys.The results show that the microstructure analysis of the as-cast alloys shows that(Al,Si)3(Zr,Ti)and?-Fe phases formed.Compared with the Al Si7Mg0.4 alloys without Zr,the alloys with Zr have smaller grain sizes.The alloys with Zr precipitate(Al,Si)3(Zr,Ti)strengthening phases during the solution treatment.After T6 heat treatment,Mg in the Fe-rich intermetallics and a small amount of coarse(Al,Si)3(Zr,Ti)phases diffused into the matrix,which decreased the intermetallics sizes.The alloy with 0.06%Zr showed the best mechanical properties,and its tensile strength,yield strength and elongation were 332 MPa,305 MPa and 8.67%,respectively.Taking the Al Si7Mg0.4Zr0.06 alloy as the research object,the alloy was refined by using Al-Ti-C and the new Al-Ti-C-B refiner.The effects of different refiners on the as-cast and heat treatment were analyzed.Of the microstructure,mechanical properties and fracture morphology of Zr-containing alloys.The results show that when the Al-Ti-C refiner is used to refine the Al Si7Mg0.4Zr0.06 alloy,in addition to no contribution to the grain refinement,the Al4C3formed by the decomposition of Ti C will also introduce other inclusions in the melt,which affects the alloy's performance Mechanical properties;when Al Si7Mg0.4Zr alloy is refined with Al-Ti-CB refining agent,it has no obvious effect on the alloy microstructure,but the micron-level Ti Cx@TCB core-shell structure will be introduced into the structure,which will cause a certain degree of alloy elongation influences.Therefore,both Al-Ti-C and Al-Ti-C-B refiners are not suitable for refining Al Si7Mg0.4Zr0.06 alloy.The wheel of Al Si7Mg0.4Zr0.06 alloy was trial-produced by low-pressure die casting,and the microstructure and mechanical properties of the wheel were analyzed.The results show that the low-pressure die casting AlSiMg Zr wheel has excellent comprehensive mechanical properties,and the performance is better than the wheel of A356 alloy without Zr added in the literature. |
PDF Full Text Request