Continuous Drive Friction Welding Of Dissimilar Metals Between Magnesium Alloy And Aluminum

The Aluminum alloys （Al） and magnesium alloys （Mg） composite structure would allow weight reduction, further design flexibility and expand their application, so that it can be used in the field of aerospace, automotive and communication equipment. However, the welding of Al and Mg alloys has been facing a big challenge due to their different thermophysical properties. The Al/Mg fusion welded joints are not suitable for industrial application because of formation of excess brittle intermetallic compounds （IMCs）, which deteriorate the strength of Al/Mg joints. Therefore, the formation mechanism of IMCs in Al/Mg joints and how to inhibit the formation of IMCs have been a hot spot in recent years. Because friction welding has some advantages in aspect of low welding temperature and good microstructure caused by forging, friction welding is a suitable candidate for accomplishing sound joints of Al bars to Mg bars. The effects of welding parameters on microstructure characteristics and mechanical properties of dissimilar friction welding of 1060 Al and AZ31B Mg alloys were investigated. The effects of welding parameters, such as friction pressure, friction time, upsetting pressure and rotation speed, on the interfaces microstructure, temperature, IMCs formation and welding quality of the joints were studied.According to the results of experiment, it can be concluded that the joints strength increase with the friction pressure, friction time and upsetting pressure increasing in experiment range. The maximum tensile strength of the welded joints can reach up to 88% of the strength of the 1060 Al alloy base metal, about 142MPa. During the tensile test, all samples failed at the friction interfaces. The fracture mode is mainly brittle fracture.In the present study, a continuous, narrow, IMCs layer was generated on the interfaces of the Al/Mg welding joints, which indicated that metallurgical reaction occurs in the Al/Mg welded joints. However, the formation of IMCs affected the strength of joints seriously.The thin strip IMCs layer （Al₃Mg₂） formed in diffusion bonding region-â…  which mainly appears at the center zone. The thicker strip IMCs layer （Al₃Mg₂ and Al₁2Mg₁7） formed in diffusion bonding region-â…¡ which is mainly located at the half radius-periphery zone. The Al₃Mg₂ is produced near the Al side, while the Al2Mg17 grow near the Mg side.Microstructure morphology in mechanical interlocking region is an important part in the interface of joints which formed mainly at initial stage of the welding process. With friction time increasing the volume of mechanical interlocking region decreases gradually where a part of mechanical interlocking region is transferred into thicker strip IMCs layer and another part is transferred into constitutional liquation.The temperature of Al/Mg friction interface can reach up to 437℃ according to the temperature measurement, which indicated that constitutional liquation can occur in this experiment. Eutectic reaction, liquidâ†'Al₃Mg₂+Al or liquidâ†'Al₁2Mg₁7+ Mg, occurred in constitutional liquation region during Al-Mg dissimilar friction welding. There is intimate links with the formation of IMCs （Al₃Mg₂ and Al₁2Mg₁7）. In this experiment, the constitutional liquation results in distinct microconstituents: segregation structure, divorced eutectic structure, network structure and liquid-solid mixed structure.Though the constitutional liquation occurs in friction interface, friction welding still has a lot of advantages compared with other fusion welding process. The dissimilar materials Al/Mg friction welding joints can acquire good joints properties without assistant equipment and filler metal.Therefore, Al/Mg friction welding joints have a huge advantage.