Study On Characteristics Of Friction Stir Welding Of Dissimilar Materials Based On Thermal Assist And Repair Welding

Lightweight is a vital part in China’s energy conservation and emission reduction strategy.However,the traditional structural materials are difficult to meet the needs of lightweight performance.Therefore,the problem of lightweight may be solved because the metal and polymer composite structure has the advantages of light weight,low density,excellent mechanical properties,insulation properties,thermal insulation properties and excellent characteristics.Friction stir welding(FSW)has a wide range of materials and has high advantages in environmental protection,efficiency and automation,which has become a new method to connect dissimilar materials.However,the joint with neat weld and stable mechanical properties is difficult to form due to the great differences in physical and chemical properties between metal and polymer materials.Thus,new methods must be adopted to improve the cleanliness of the weld surface and ensure high strength of the welded joint.Two methods are introduced to improve due to the defects such as pores,incomplete penetration and grooves on the weld surface of FSW in connecting dissimilar materials,which is to improve the consistency of weld connection and ensure the high efficiency of welding quality.This paper takes 6061-T6 aluminum alloy and polycarbonate(PC)as the research object.Method 1: The thermal assist method is accepted to low the difference of temperature gradient between the two materials during welding,so as to improve the surface appearance,improve the joint property and improve the practical value of samples;Method 2: The repair welding method is adopted using two less tool with different shoulder diameters to promote the full and uniform stirring of the two materials,so as to improve the plastic fluidity of the two materials and decrease the welding defects.The purpose of improving the FSW welded joint of 6061-T6 aluminum alloy and PC material is achieved through the above two methods.The experimental results show that the welded joints with smooth surface,good appearance and less defects can be obtained by two methods.In the aspect of mechanical properties,the tensile strength which is equivalent to 68% of the base metal can be obtained by thermal assist,and the hardness of the joint increases after thermal assist except the thermal assist of 100℃.For the repair method the average tensile strength of the two repair welding joints increased by 0.61% and 14.43% respectively.Besides,the hardness value of the repair welding joint is equivalent to that of the non repair welding joint for 16 mm shaft shoulder,which is to ensure that the joint quality.Finally,the micro inspection of the welded joints based on the two improved methods is carried out respectively.The differences between the internal structure and composition of the weld are analyzed and compared.The results show that thermal assist can promote the full stirring and mutual mixing of the two materials in the nugget zone.Repair welding can effectively fill the holes and grooves at the bottom of the nugget area.Besides,there is an obvious upward flow trend of material in the vertical direction of the nugget.