Study On Friction Stir Lap Joining Of 6061-T6 And Zinc-Coated Steel

In the automobile production industry,although aluminum alloy and galvanized steel plate are more and more widely used in the main structural parts,but the use of traditional melting welding method welding is easy to produce defects.Therefore,friction stir welding is an important process for aluminum-steel heterogeneous metal welding.However,there are few researches on the friction stirring lap welding technology of aluminum-steel heterogeneous metal sheet,and the connection of aluminum-steel heterogeneous metal sheet with thickness of 1mm is successfully realized under the condition of small axial force by using the ultra-high speed stirring friction stir welding machine developed by independent in this paper.Although the high speed reduces the axial force during the welding process,the temperature and axial forces at the interface of the aluminum-steel sheet are still playing a key role in the production of aluminum-steel intermetallic compounds,and the pin length of the tool is an important factor affecting the interface temperature and pressure.Among them,aluminum-steel intermetallic compounds can effectively connect the two sides of the metal,but aluminum-steel intermetallic compounds are brittleness,and in the addition of the middle layer can effectively organize the production of intermetallic compounds,and the use of aluminum zinc solid solute and zinc iron intermetallic compounds to achieve connection.Four kinds of tools with different pin length were used to test the welding process of6061-T6 sheet and galvanized steel sheet.It is found that the axial force range from 0.2kN to 1.1kN in the whole welding process is much smaller than that produced in friction stir welding at conventional rotational speed.At the same time,the longer the pin length of the tool,the fuller the plastic flow of the base material,the higher the thermal input generated during the welding process,but also will lead to the axial force from the spindle in the plastic flow of the base material media can hardly be fully transmitted,and thus reduce the axial force of the interface,and the pin length is shorter although the pressure transfer is more adequate,but the heat production is less.How to find the optimal parameters in these two factors to obtain the best mechanical properties of the joint is the first problem to be solved.After comparison test,it is concluded that when the tool with pin length of 0.3mm,the welded joints with the best mechanical properties are obtained.The interface characteristics of welded joints with the best mechanical properties obtained by welding with different tool with different pin length are analyzed.After analysis and detection,it is found that the metal compounds with equal thickness are generated at the interface of the welded joints,and the main components are Fe₄Al₁₃.In the joint connection,the Intermetallic compound plays a major role.However,due to the different temperature and axial force of the interface when using different pin-length tool,the thickness of the intermetallic compounds formed by the interface is different,only the use of tool with pin length of 0.3mm,the resulting welded joint interface intermetallic compound thickness is the largest,and the most uniform,so the best mechanical properties.The fracture observation found that the intermetallic compound has a certain brittleness,so also through the bonding interface to add different thickness of zinc foil between two metal sheet bonding friction stir welding process test,the intermediate zinc layer on the aluminum-steel heterogeneous alloy friction stirring welding joint interface characteristics and the effect of the mechanical properties of the joint.It is found that compared with aluminum-steel heterogeneous alloys without zinc foil,zinc foil with moderate thickness can effectively isolate the direct contact between aluminum and steel and reduce the production of brittle intermetallic compounds such as Fe₄Al₁₃,but through the aluminum zinc solid solute and zinc iron intermetallic compounds to achieve the connection.The ultra-high speed stirring friction welding can weld the aluminum-steel sheet and obtain the effective joint under the condition of small axial force.The use of the tool with short pin length is suitable for direct bonding of aluminum-steel sheet with thin middle layer,so that the interface produces aluminum-steel intermetallic compounds with uniform thickness,but on the basis of this process,adding middle layer in the interface can effectively inhibit the production of intermetallic compounds,The mechanical properties of the joints were further improved by the connection between the aluminum zinc solid solute and the zinc iron intermetallic compound.