Effect Of MIG Welding Process And Post Weld Heat Treatment On Microstructure And Mechanical Properties Of Al-12.7Si-0.7Mg Welded Joints

Compared with6063aluminum alloy widely used in many fields, Al-12.7Si-0.7Mg alloy has more excellent mechanical properties. In this study,3mm thick hot extruded Al-12.7Si-0.7Mg alloy plates were welded by automatic MIG welding method using imported ER4047welding wire. The influence of changing heights of nozzle on weld formality and gas pore was researched. After welding experiment, the welded joints were treated though solution treatment and artificial aging. Then, microstructure and mechanical properties of welded joints before and after post weld heat treatment were studied by OM, TEM, microhardness and tensile test methods. Besides, the crack tendentiousness of hot extruded Al-12.7Si-0.7Mg alloy plate was judged though the fishbone cracking test method.The main results obtained though out studies are listed:1. The optimum welding parameters of MIG method is applied for55cm/min welding speed,100A welding current,19V welding voltage,1%arc length,4.6m/min wire feeding speed and the height of10mm nozzle. The great welded joints with good formality and less gas pore were acquired according to parameters above.2. The microhardness of welded joints which were treated by solid solution and artificial aging increased. Meanwhile, the position of lowest microhardness appeared at weld zone. The strength of welded joints was also enhanced a lot after solid solution and artificial aging. The best tensile strength of welded joints was obtained at solid solution at520℃for1.5hour and aging at180℃for3hours. Under such condition, the yield strength and ultimate strength of the joints reached277MPa and340MPa, respectively. Compared with the welded joint before heat treatment (yield strength and ultimate strength are106MPa and189MPa, respectively).The enhancement of yield strength and ultimate strength are respectively22.7%and78.3%.3. A lot of needle precipitate phases which played the role of precipitation strengthening were discovered in weld zone of joints after solid solution at540℃for1.5hours and aging at180℃for3hours.The size of needle precipitate phases is about50～150nm.4. No crack was appeared in the surface of welded joint after the fishbone cracking test. Therefore, this material has low crack tendentiousness and good anti cracking performance.