The Study On Strengthening And Toughening Of Al-Si-Cu-Mg Alloys Based On Composition Optimization

Since the beginning of the 21st century,China's aerospace industry has experienced a rapid development process,casting aluminum alloy has been widely used in the field of aerospace because of its good mechanical properties.In recent years,the requirement of materials in aerospace field has changed from lightweight to toughening.In order to further improve the mechanical properties of Al-Si-Cu-Mg cast alloy,this work focus on the achievement of good mechanical properties by optimizing the content of main alloy elements,adding sodium salt and Sr modifier,adding rare earth Y and T6 heat treatment.The mechanism of strengthening and toughening of the alloy were studied and analyzed.Firstly,in order to determine the range of the main elements in the alloy,the effect of the interaction of the alloy elements on the mechanical propertiesof the alloy in the range of(8,9,10)wt%Si,and(0.5,1,1.5)wt%Cu(0.3,0.4,0.5)wt%Mg was studied by orthogonal experiment;the strengthening mechanism were also analyzed.The results showed that Mg and Cu have the greatest influence on the tensile strength of the alloy,and the effect of Si on the elongation was significant.the Al-10Si-1Cu-0.4Mg alloy had a better comprehensive mechanical property than other compositions,the tensile strength was 275MPa and the elongation ratio was 3.2%.Al 2Cu was the main strengthening phase to improve the mechanical properties of the alloy.Secondly,the compound modification of Na and Sr on Al-Si alloy and the mutual influence of these two kinds of modifiers was studied when the sodium salt and Al-lOSr master alloy were added.The results indicated that combining additions of Na and Sr have synergistic effects on eutectic silicon.However,combining additions of sodium salt and Al-10Sr changed the absorption rate of Na and Sr,and the presence of sodium salt could lead to Sr both content and absorption drop significantly,while Sr promoted the absorption of Na.It was considered that such difference was resulted from the reaction between sodium salt and Sr.The modification effect was determined by the contents of Na and Sr.For Al-Si alloy containing Si 9 Wt%,combining additions of(10ppm-12ppm)Na and(48ppm-99ppm)Sr could get a better modification effect.Lastly,the effect of Y on the microstructuresand properties of the alloy was studied by adding rare earth Y.the results showed that the tensile strength and elongation of the alloy increased first and then decreased with the Y contents increase.when the Y content was stable at 0.3%,The tensile strength and elongation of the alloy reached the maximum,the tensile strength and elongation were 315MPa,4.2%,respectively.The eutectic silicon size was the smallest and the most uniform when the content of Y was 0.3%and the proper amount of Y could refine the eutectic silicon.