Structure And Performance Of FSW Joint Of Al Alloy And Mg Alloy

Friction stir welding (FSW) is a patented new solid joining process, which was invented at TWI ten years ago. At present, in developed countries the friction stir welding process is already in commercial use, but it is just beginning in our country. The study on friction stir welding of Al alloys and Mg alloys sheet were conducted with self-made equipment. The study will provide the bases of theory and practice for wide application of friction stir welding in our country.The design of welding head geometry is the key for friction stir welding. The friction stir welding using cylindrical stir-welding head was conducted, and according to literature confirm that the optimal size of cylindrical stir-welding head for 8 mm thick Al alloys and Mg alloys plate is that the diameter of shoulder is 24 mm and the diameter of welding-pin is 8 mm. The optimal size of cylindrical stir-welding head for 1.5 mm thick Al alloys plate is that the diameter of shoulder is 10 mm and the diameter of welding-pin is 2 mm.Effects of welding speed and tool's roating speed on the structure of joints and tensile strength, hardness, fracture toughness were investigated. Good weld shaping ia achieved if welding matches well with rotating speed,and the coefficient of tensile stength can be up to 85.4% for 8mm thick LF21 Al alloys plate,32.7% for 8mm thick AZ31B Mg alloys plate and 91.3% for 1.5mm thick 6K32-T4 Al alloys plate. the microstructure of fracture was observed.It can be found that tendency to brittle fracture is obvious in weld nugget and the slight plastic fracture characteristics can be found in partial regions. Furthermore,through micro-hardness inspection hardness on HAZ reduces greatly in comparison with base metal,and hardness in both TMAZ and weld nugget vary to some extent. The results of fracture toughness show that Al alloys have very excellent fracture toughness after FSW and Mg alloys fracture toughness was not as good as Al alloys. Bi-friction stir welding(Bi-FSW) was put forward, at the same time studied it's microstructure and hardness.