Study On The Mechanism Of Ti And Zr Inoculant Refinement Of Al-Cu Alloys

Al-Cu alloy are widely used in the aerospace, marine, lightly armored andtransport vehicles and other industrial applications with its excellently hightemperature and low temperature performance. With the increase of the moreextensive application, the properties of Al-Cu alloys are put forward higherrequirements. So, it is necessary to take effective measures to improve theperformance of Al-Cu alloy. Grain refinement is one of the most effective means toincrease the strength and plasticity, and achieve comprehensive mechanical propertiesof the alloys. In industrial production, adding grain refiner in solidification process toprovide numbers of heterogeneous nucleation is the most simple and effective way torefine grains of the alloy.This article is undertaken to investigate the morphology of the microstructureand nuclei, alloy phase, and nucleation temperature by separately and compoundadding trace Ti, Zr elements in Al-Cu alloys. So it can be explored the grainrefinement mechanism of inoculant Ti, Zr on Al-Cu alloy. The major findings hasmade as following:The effect of compound inoculants Ti and Zr on Al-Cu alloy is compatible.Without any inoculants, the microstructure of alloy are made of coarsely branchescrystal; When Ti or Zr element added alone, the microstructure of alloy aretransformed into equiaxed grain; When Ti, Zr composite added and the total mountsof Ti, Zr inoculants total being equivalent with Ti or Zr added alone in Al-Cu alloy,the grains achieve further refinement; and with the content of Ti, Zr compositeaddition gradually increased, the grain refinement effect is further increased. Whenadding w(Zr)=0.1%and w(Ti)=0.5%, the alloy has fine crystal grains and the highesttensile strength of alloy(181MPa).When the composite content of Ti and Zr is higher in Al-Cu alloys, twocomplexes appear in the alloy, one is Al3(Ti, Zr) complex phase which consists ofthree elements Al, Ti, Zr. Another is dual-particles which is formed by Al3Ti phaseattached surface of Al3Zr phase. By analysis: the complex Al3(Ti, Zr) phase can beacted as heterogeneous nuclei. Al3(Ti, Zr) phase can promote-Al heterogeneousnucleation by peritectic reaction: L+Al3(Ti, Zr)â†'-Al, the peritectic reaction temperature is685.7℃. At the same time, with decreasing of the melt temperature, theAl3Ti layer of the dual-particles occur peritectic reaction with aluminum:L+Al3Tiâ†'-Al, it promotes heterogeneous nucleation of-Al.When the content of inoculants Ti and Zr is less in the Al-Cu alloy, Al3Ti andAl3Zr phase will be the main heterogeneous nuclei to promote the heterogeneousnucleation of-Al; When the composite content of Ti and Zr is higher in Al-Cu alloys,except for the finer Al3Ti and Al3Zr phase acting as heterogeneous nuclei, thecomplex compounds Al3(Ti, Zr) phase and dual-particles formed in the melt can alsobe the heterogeneous nuclei and promote the heterogeneous nucleation of-Al.