Influence Of Welding Process On Microstructure And Mechanical Properties Of Al-2.7Si-0.7Mg Alloy Joints Welded By Friction Stir Welding

Friction stir welding is a new solid-state joining technique, which has lots of prominent advantages, such as high quality, low deformation and low cost. It is the priority welding method for Aluminum alloys. Recently, a high-Si Mg-containing wrought aluminum alloy has been developed. Compared with6063aluminum alloy, this new developed wrought Al-Si alloy has excellent mechanical properties and very good application prospect. However, the research on this material’s properties by friction stir welding has not carried out.In this study, the base material used was a3mm thick Al-12.7Si-0.7Mg alloy plate cut from hot extruded Al-12.7Si-0.7Mg alloy profiles. The welding samples were welded by friction stir processing (FSP). The downforce of stir tool and the temperature of weld center were measured at the fist real-time in the welding process. The microstructures and welding defect of FSP welded joints were analyzed by X-ray detection, microstructure observation and heat input value calculated, then obtained the optimum match rang of welding parameters. Analyzed microstructure and mechanical properties of FSW joints welded in the optimum rang of FSP welding parameters. Furthermore, welded Al-12.7Si-0.7Mg alloy plate by friction stir processing with welding equipment transformed from a traditional milling machine, and acquired the Z-axis mechanical signals curve of entire welding process through self-designed experiment measuring table.The following main results are obtained:1. Two mainly kinds of defect such as fin and hole defect in joints at the choice welding parameter by friction stir processing. Controlled heat input from2.39μπJ to7.09μπJ can avoid these welding defects, and obtained following welding parameters:(1) Welding speed from200mm/min to400mm/min while rotation speed is600rpm.(2) Rotation speed from1200rpm to2000rpm while welding speed is800mm/min.(3) Rotation speed range from600rpm to800rpm while welding speed is200mm/min. 2. Microhardness of the welded joints in Nugget was higher than TMAZ, HAZ and retreating side is higher than advancing side. A soften region with lower microhardness exits in the TMAZ of advancing side.3. The welded joint with the best tensile properties, good forming and without defect that was welded by FSW with friction stir tool rotation speed600rpm and welding speed200mm/min. Under the above welding parameters, the ultimate strength of the welded joint is197.5MPa (reaching100.76%that of the base material), the yield strength is107.5MPa and elongation is9.94%.