Effect Of ECAP Route On Microstructure And Mechanical Property Of Al-Mg-Si Alloy

ECAP is an effective method to process ultra-fine bulk grain material by deforming the material similar to simple shearing the same sample may be pressed repetitively to attain exceptionally high strains and to get much finer and more uniform microstructure. It has been shown that ECAP processing can play a dual role by both refining grain size and also significantly altering the precipitate morphology. According to the rotation around the longitudinal axis of the sample, different processing routes are developed. There are four basic routes, namely routes A, BA, Bc and C. It has been shown that the processing route has a significant influence on the efficiency of ECAP processing in microstructural refinement as well as in fragmentation and redistribution of precipitates.We have known that the Al-Mg-Si alloy consists ofα-Al and Mg2Si phase. In this paper, the Al-5Mg-2.5Si, Al-5Mg-2Si were cast and then ECAPed for 8 passes by routes 8BA,8Bc,8BC-UD2 and two different combination-type routes 4BA+4BC and 4BC-UD2+4Bc using a die withmφ=90°at 200℃and 2mm/min. Their microstructures after different ECAP routes were investigated by optical microscope (OM), the mechanical properties were measured by tension at room temperature. Also, we observed the fractograph of Al-5Mg-2Si alloy tensile sample.Pure aluminum and the two-phase Al-5Mg-2.5Si alloy were pressed by ECAP processing for 1 pass at room temperature and 200℃respectively. It is shown that the pressing speed has no effect on the microstructure of pure metal or alloys. And, the deformation is pure shear deformation, nearly. The experimental results show that route BC exhibits a poor effectiveness for particle redistribution while routes BA and BC-UD2 usually result in an elongated microstructure with an orientated alignment of the precipitates, especially in the case of route BA. The combined routes 4Bc_UD2+4BC,4BA+4BC exhibit a remarkable particle redistribution effectiveness in comparison with the conventional route BC-Mg2Si particles are distributed dispersedly in the matrix and the ductility and the toughness of the composite are greatly enhanced.The result of tension test shows that the alloy through resolved and aged condition had poorer tensile strength and elongation. However, Tensile strength and elongation remarkablely increased respectively after ECAPed. The increase in the tensile strength and ductility of the ECAPed Al-Mg-Si alloy is due to the remarkable refinement in the matrix and the morphology and the distribution change of Mg2Si by ECAP. The strength of routes 4BC-UD2+4BC,8BC-UD2,4BA+4Bc and 8BC is better than the route 8BA, and the elongation of the route 8BC is poorer than the other routes. The analysis of fractograph showed the dimple-like fracture characteristics of the Al-Mg-Si ECAPed alloy clearly. Also, the alloy puts up some characteristics of quasi-cleavage fractures by Bc route. The fractograph of 4BC-UD2+4BC,8BC-UD2,4BA+4BC and 8BA routes is much more than 8BC route, also equiaxed and distribute more homogeneously.