Research On Microstructure And Mechanical Properties Of 5A06 Aluminum Alloy Resistance Spot Welding Joint

Compared with the steel and other materials, the aluminium alloy has many advantages, such as lower density, lighter weight, higher specific strength, resource-rich, smaller rotary torque, better corrosion resistance and low production cost. According to the increasing demand for lightweight structures in recent years, it has becoming an inevitable trend using aluminum alloy materials to replace steel in some areas. However the aluminum alloy is limited to its poor welding performance. Thus the welding technology of aluminum alloy become one of the key technologies which the aluminum alloy will be widely used for welding structure.At present, the research on the performance of 5A06 aluminum alloy sheet resistance spot welding joints were relatively rare. The resistance spot welding joints fracture microstructure and characteristics of 5A06 aluminum alloy were extensively studied in this paper. The influence of electrode pressure, welding current and welding time on the properties of the spot welding joints, the forms of breakage and the second phase in the joints were studied in detail and the results showed that:There are two main forms of breakage of 5A06 aluminium alloy spot welding joints. Respectively are joint fracture tow and button fracture. When the welding current was too small(less than 23 k A), the joint fracture was liable to happen. While the joint fracture occurred, the fracture was neat with metallic luster. Its maximum shear resistance was far less than the design requirements. So we should try to avoid the appearance of joint fracture. When a button fracture occured, it was mainly torn along the heat affected zone or the base metal, micro-fracture showed the tearing rib existed obviously in the start-off position.When welding pressure increased from 2.8k N to 3.3k N to 3.8k N, welding current increased from 23 k A to 24 k A to 25 k A, welding time increased from 130 ms to 140 ms to 150 ms, the range of equal axis crystal region, the maximum shearing resistance of joint, the diameter of nugget(except the change of the electrode pressure) and the number of second phase particles in a joint all showed a trend of first increases and then decrease. The micro-hardness showed a trend of decrease then increase last decreased. When the electrode pressure changed, the core diameter of the nugget was gradually decreasing. From the XRD figure showed that there was no new diffraction peaks appeared both before and after welding in which there was no new phase appeared.