Study On IMCs Control Of Friction Stir Welding Joint Of Al/Mg Dissimilar Alloy

With the rapid development of green manufacturing and structural lightweighting,friction stir welding of aluminum alloys and magnesium alloys has been widely used and developed rapidly in transportation,aerospace,shipbuilding and other fields.However,because friction stir welding of aluminum alloy and magnesium alloy easily generates brittle and hard IMCs in the joint and further evolves into a compound layer,which greatly reduces the performance of the joint.Therefore,how to suppress and reduce IMCs in the process of friction stir welding of aluminum/magnesium dissimilar alloys the important and difficult points of the current research.Starting from suppressing and reducing brittle and hard intermetallic compounds and improving joint performance,this paper takes 2024-T3 aluminum alloy/AZ31 B magnesium alloy as the research object to carry out process parameters and filling third-party metal sandwich friction stir welding experiments,the effect of process parameters,filler metal type and thickness,and bimetal interlayer on joint performance is systematically studied,and discuss the influence mechanism of filler metal interlayer on IMCs of friction stir welding joints of aluminum/magnesium dissimilar alloys.Firstly,a special fixture was designed to study the reasonable process parameter range of friction stir welding for 2024-T3 aluminum alloy and AZ31 B magnesium alloy.By comparing the surface morphology and tensile strength results,it is found that the joint quality of the stirring head with a shaft shoulder diameter of 10 mm is not ideal,and the joint strength of the stirring head with a shaft shoulder diameter of15 mm at a rotation speed of 300/min and a connection speed of 30mm/min is the highest.Based on the results of the process parameter experiment,the 2024-T3 aluminum alloy/AZ31 B magnesium alloy interlayer friction stir welding filling experiment with a shaft shoulder diameter of 15 mm under the conditions of a rotation speed of300r/min and a connection speed of 30mm/min was carried out,it is found that as the thickness of the metal layer increases,the quality of the joint becomes worse and worse.When the thickness of the metal interlayer is 0.1mm,the joint performance is the best.When the thickness of the interlayer is increased to 0.5mm,the joint cracks and even cannot be formed.Subsequently,the friction stir welding joints filled with different metal types were studied mainly with a metal interlayer with a thickness of 0.1mm,it is found that adding a 0.1mm Cu layer has the lowest tensile properties of the joint.Through EDS and XRD analysis,it is found that a small amount of Cu in the joint reacts with aluminum alloy to form Al Cu4,most of them are still continuously distributed in the butt joint of the base metal in the form of simple substance,although the contact reaction of the base metal is inhibited,and the connection of the base metal is more fragile;the strength of the 0.1mm thickness Ni layer is slightly lower than that of the base material,EDS analysis found that the Ni layer is intermittently distributed in the joint in the form of lumps and granules of different sizes,because of the high melting point,it does not react with the base material,and at the same time suppresses the gap between the base materials,the reaction effect is very small,causing the base metal connection to be more fragile;Only the 0.1mm Zn layer is stronger than the base material,the Zn layer is alternately distributed in layers in the joint,forming Mg Zn2 with the magnesium alloy on the magnesium side,inhibiting the formation of intermetallic compounds between the aluminum alloy and the magnesium alloy.Under the same process parameters,the effect of bimetallic interlayer on the performance of aluminum/magnesium dissimilar alloy friction stir welding joints was studied,when filling both Zn and Cu layers with a thickness of 0.1mm at the same time,placing Cu on the magnesium alloy side and Zn on the aluminum alloy side,the tensile properties of the joint are greatly improved.The Cu layer and the Zn layer are strip continuous distribution in the joint butt,the analysis found that the Zn layer reacts with the Cu layer to generate Cu Zn2 and generates Mg-Zn compounds such as Mg-Zn2 with the base material,and the Al-Mg brittle and hard intermetallic compounds are greatly reduced.