Study On Microstructure And Mechanical Properties Of FSW Joint Of 5A06 Aluminum Alloy

Weapons equipment manufacturing industry is of great significance to improve the national equipment manufacturing industry and national comprehensive strength. Underwater weapons pursuit rapid, sensitive and resistant to corrosion, resistance to stress. Aluminum alloy of 5A06 is used for the material of a certain water weapon. The traditional connection method is the fusion welding, which can cause the joints softening, porosity and slag inclusion, that will reduce the service life of the weapon in the water. FSW is a novel solid-phase welding, which can avoid fusion welding defects, and improve product quality. Therefore, the study of FSW parameters of 5A06 aluminum alloy is of important significance.The influence of engineering factors and process parameters on joints surface morphology and mechanical properties were studied. Microstructures of joints of different regions were observed by using OM and SEM. Components of base metal and friction string welding joints were analyzed by X ray diffraction(XRD). FSW joints cross-section in the thickness direction and along with the welding hardness were tested by Vickers hardness tester; And FSW joints tensile strength at room temperature static load were tested by tensile testing machine. Tensile fractures were observed by SEM. The results were as followed:Engineering factors and the parameters were combined influencing the joints surface morphology. For 5A06 aluminum alloy sheet with the thickness of 5 mm gap less than 0.2 mm, plate difference controlling less than 0.2 mm and pin in depth in 0.3 mm, welding pressure in 28~30kN, rotational speed in 400~480r/min and welding speed in 20~45cm/min were obtained a good surface morphology. The welding joints of aluminum alloy 5A06 can be divided into four regions. They respectively were base metal(namely BM) heat affected zone(HAZ) weld nugget(NZ), and thermal mechanically affected zone(TMAZ). The grain of parent material was elongated along the rolling direction and the grain was uniform and coarse. The grain size and grain boundaries of the heat affected zone were coarser than that of the base metal. Grain size was not uniform and grain morphology was different at TMAZ. Because dynamic recrystallization occurred in weld nugget, so grain was uniform and fine. On the advancing side, the boundary between the weld nugget area and the thermal mechanically affected zone was clear, while on the retreating side the boundary between these areas were blurred. FSW joints and base metal phase compositions were Al and Mg2Al3. There was no new phase appearing in FSW and the diffraction peak fundamental did not change and no new peak generation, but the intensity of the diffraction peaks changed. The hardness curves of welding joints cross section showed "n" type distribution. Plastic fracture occurred in base metal at the absence of welding defects.