Microstructure And Mechnaical Property Of High-mg₂si Al-mg-si Alloys By Severe Plastic Deformation

Al-Mg-Si allay is a widely applied aluminum alloy now. Intermetallic compound Mg2Si, as an excellent reinforcing phase, can raise the strength of alloys, But there are small amount of Mg and Si(Si: 0.3% ~1.3%wt.,Mg: 0.35~1.4%wt.) in traditional Al-Mg-Si allay ,and the amount of reinforcing phase Mg2Si is also few.The reason of don't through increasing the amoune of Mg2Si to raise the strength of alloys is that the intermetallic compound Mg2Si distributed along the grain boundary as the large Chinese script or skeleton-shaped in as-cast microstructure. the large Chinese script or skeleton-shaped Mg2Si greatly dissevers the matrix and leads to the decrease of the ultimate tensile strength and the elongation.ECAP is an effective processing to refine grain.It can impose severe plastic deformation on materials in the simple shearing model to obtion ultrafine-grained bulk materials.In this paper, through increasing the amount of reinforcing phase Mg2Si in Al-Mg-Si allay and combined with ECAP processing to refine the matrix and break Mg2Si phase to prepare excellent comprehensive properties Al-Mg-Si allay of higher amount of Mg2Si;Then exploring the way of Sb modification combined with ECAP to raise the strength of alloys;at last, making a study on the enhancement of aging treatment to ECAPed alloys.Al-5Mg-2Si,Al-10Mg-Si and Al-10Mg-4Si-0.8Sb alloys were casted in this experiment and these alloys were was ECA pressed through some passes at 250℃in route Bc. Phase constituents were determined by XRD. The microstructures before and after ECAP were investigated by scanning electron microscope (SEM) and transmission electron microscope (TEM). The mechnical property of alloys before and after ECAP were measured through tension test and hardness test.The results of XRD phase analysis show that Al-Mg-Si alloys are consist ofα-Al and Mg2Si phase ;The result of scanning electron microscope (SEM) and transmission electron microscope (TEM) investigation show that the as-cast microstructure of the alloy was very coarse, with the large Chinese script or skeleton-shaped Mg2Si distributed along the grain boundary; The as-cast microstructure after modification treatment was refined to some extent, the size of reinforcing phase Mg2Si was also finer, but the refining effect was not significant. Through ECAP processing, the matrix grain of these alloys were significantly refined. The initial coarse Chinese-script-shape Mg2Si was obviously broken into fine rod-shaped or polygonal particles and the distribution became more dispersed; through ECAP, the refining effect of Al-10Mg-Si containing higher amount of Mg2Si was superior than Al-5Mg-2Si,The reason is that more content of intermetallic compound Mg2Si have greater promotion on matrix grain refinement.The result of tension test and hardness test show that the alloy of as-cast had poor hardness, tensile strength and elongation. It is determined by the morphology and distribution of Mg2Si, The Al-10Mg-4Si-0.8Sb of after Sb modification treatment had better mechnical property than Al-10Mg-Si alloy, It is because that Sb can improve the as-cast microstructure; After ECAP, The hardness, tensile strength and elongation of all Al-Mg-Si alloy were remarkablely increased. For the same composition alloys, the hardness and tensile strength of alloy after ECAP for 4 passes were superior than those of alloy after ECAP for 8 passes,but the elongation was descrease a little.For the same passes. the hardness and tensile strength of Al-10Mg-Si was superior than those of Al-5Mg-2Si.It told us that more amount of fragmented Mg2Si more enhancement effect for Al-10Mg-Si alloys. The tensile strength of Al-10Mg-4Si-0.8Sb alloy after Sb modification was superior than Al-10Mg-4Si alloy ;Aging treatment is useful for the enhancement of Al-Mg-Si alloy, After ECAP 8 passes, The tensile strength and elongation of Al-10Mg-4Si-0.8Sb after aging treatment was increased greatly.