A Study On Microstructure And Property Of Al-Si-Li-Mg Alloy

As a kind of new lightweight high-strength aluminum alloy,Al-Li alloy has been widely used in aerospace and other fields.In the development process of Al-Li alloy,it still has its own limitations.This topic innovatively takes Si as the main alloying element in Al-Li alloy,explores and develops a new Al-Li alloy system.By changing the Si content in Al-Li-Si-Mg alloy,the microstructure of the casting alloy was analyzed.Then by fixing the 3%Si content and increasing the Li content,the microstructure changing law of the casting alloy was analyzed,so as to further reduce the quality of the alloy.In addition,the heat treatment process,the mechanical properties and the density of Al-yLi-3Si-Mg alloy were explored.Researches show that:After 3%Si was added to the Al-3Li-Mg alloy,a new AlSiLi phase precipitated,which formed eutectic structure with?-Al.After Si content exceeded 3%,massive primary AlSiLi phase began to precipitate out of the as-cast structure of Al-3Li-xSi-Mg alloy.With the gradual increase of Si content,the size of massive phase gradually increased and tended to triangulate.The addition of Si had little effect on the alloy density.After the addition of1.5%Li to Al-3Si-Mg alloy,the precipitation of Si and Mg₂Si phases was inhibited,and AlSiLi phase began to precipitate from the alloy.With the increase of lithium content,AlSiLi phase content increased.When the lithium content was 3.5%,AlLi phase precipitated out,the AlSiLi phase content decreased,and the AlLi phase was prone to oxidation,showing a continuous distribution of black patches at the grain boundary.When the lithium content increased to 5.5%,the alloy was mainly composed of?-Al and AlLi phases,and the AlSiLi phase basically disappeared.The density of the alloy decreased obviously with the increase of lithium content.The eutectic AlSiLi phase was difficult dissolvable phase.With temperature rising and homogenization processing time increasing,its degree of solubility increased gradually.Homogenization treatment for 16 h under 550?was better.AlLi phase was easy to oxidize and dissolve.It could be completely dissolved when handling for 16 h under 530?.The burnt point of Al-3Si-3Li-Mg alloy was between 550?and 605?.The optimized heat treatment technology was solid solution treatment?550?16 h?and aging treatment?185?12 h?.The Vickers hardness of Al-3Li-3Si-Mg alloy in the artificial aging state increased with the aging temperature increasing,and the aging hardening curve presented double-peak characteristics.