Effect Of Trace Element Ce On Microstructure And Properties Of Al-Mg-Si-Cu Alloy

Al-Mg-Si-Cu alloys are widely used in automotive and aerospace industries for their light weight,good formability,and high overall performance,and are key materials for achieving industrial lightweighting.The addition of Cu can significantly improve the strength of the alloy,but the development of Al-Mg-Si-Cu alloy is hindered by the existence of serious intergranular corrosion tendency.Therefore,in this paper,based on the composition of alloy 6013,the effect of Ce microalloying on the microstructure,mechanical properties and corrosion performance of Al-Mg-Si-Cu alloy was investigated by regulating and optimizing the alloy composition,reducing the content of Cu,adding trace amounts of rare earth elements Ce,and using the effects of rare earths such as densification,purification and refinement.The main findings of the paper are as follows.（1）The addition of trace element Ce can effectively refine the grains and reduce the number of primary phases.With the increase of rare earth content,some grains grow.With the addition of 0.2 wt%rare earth Ce,the grain size was 60-90μm,which was smaller than the grain size of the matrix alloy（110-140μm）and the 0.4Ce（70-110μm）alloy,and the large amount of Mg2Si phase within the crystal was reduced,and the Ce rich metal compounds were precipitated on the grain boundaries,and the increase of Ce rich metal compounds reduced the enrichment of Ce at the solid-liquid interface,thus making the grain refinement effect decreases.In the organization after homogenization annealing,the Mg₂Si phase is melted back into the matrix;after adding trace amounts of rare earths,the coarse needle-like Al（Mn、Fe）Si phase at the grain boundaries of the matrix alloy is transformed into a Ce rich lumpy and thin strip distribution at the grain boundaries,i.e.,the best annealing process is560℃and holding time is 24 h.The hardness reaches a peak of 70 HV.（2）When investigating the effect of Ce on the aging precipitation behavior of Al-Mg-Si-Cu alloy,it was found that Ce did not change the aging precipitation sequence of Al-Mg-Si-Cu alloy,i.e.,supersaturated solid solution-Mg/Si atomic clusters-formation of GP zone-needle-likeβ"phase-rod-likeβ’phase,but accelerated the aging precipitation process of the alloy,the GP zone andβ"phase were finer and theβ"phase In the hardness test,the alloy reached a peak of 119 HV at 180°C for 7 h in single stage aging,and the 0.2Ce alloy had a longer peak aging stabilization phase in the later stage of aging;meanwhile,the CeAlSi phase was generated in the alloy with the addition of rare earths,and the CeAlSi phase is a hard and brittle phase.The strength of 0.2Ce alloy is 412 Mpa,which is 11.4%higher than that of the base alloy,and the strength of 0.4Ce alloy is 400 Mpa,and a large number of smooth decoupling surfaces appear on its fracture surface.（3）Rare earth Ce can significantly improve the wear resistance and corrosion resistance of the alloy.After adding rare earths to the alloy,the friction coefficient is greatly reduced.With the increase of rare earth content,the friction coefficient first decreases and then increases.In the peak aging stage,the white particles on the grinding surface of rare earth alloy basically disappears,the surface is smooth,and the"furrows"of different depths appear,and the abrasive wear is dominated by the abrasive wear,and the spalling layer appears on the surface of the base alloy,i.e.the abrasive wear accompanied by spalling wear.In the intergranular corrosion,the intergranular corrosion depth of 0.2Ce alloy is 259μm,which is lower than the 314.3μm of the base alloy and 283.3μm of 0.4Ce alloy.Along with the increase of rare earth content,the coarsening of precipitation phase in the alloy and the generation of a large number of rare earth metal compounds increase the corrosion sensitivity of the alloy and reduce the corrosion resistance of the alloy.