Microstructure And Properties Of Dissimilar Materials Al/ Cu Lap Joint Byfriction Stir Braze Welding

Recently, Al/Cu dissimilar metal Friction stir welding has been the focus in modern engineering application. It is differernt to obtain high quality welding joint by traditional friction stir welding because intermetallic could be formed at the interface easily. 1A99 aluminum plate(2 mm in thickness) and H68 brass and pure copper plates(0.2 mm in thickness) were successfully lap-jointed by friction stir welding using 0.2 mm Zn sheet as filler material. Good-formability and high-quality Al/Cu joint could be achieved in the experiment.In this article, both pin and pinless tool were used to joint the dissimilar aluminum and copper. The pin was not penetrated into the bottom H68 brass plate. Good-formability joint was obtained by reasonable welding parameters. The joint macro formability and macro defects in the joints had close relationship with the rotation speed(n), welding speed(v) and the ratio(?) between v and n. In the welding process, the peak temperature at the interlayer which was underneath the weld nugget zone(SNZ) was higher than the Zn melting temperature. It was easier for the melted Zn to be extruded, mix, diffuse and dissolve to form metallurgical joint which had better mechanical property.Pinless tool was used to weld the aluminum plate and pure copper plate, in the weld configuration the aluminum was the upper plate. In the experiment, there was no macro defect found in the joints. The thickness of the interlayers decreased with with the increase of the heat input. In the two groups, the thickness decreased from 200 ?m to 9 ?m, and from 155 ?m to 8 ?m, respectively. The influence of rotating speed increment on the thickness of interlayers was greater than welding speed decrease. The temperature monitoring during the experiment indicated that under some welding conditions the peak temperature during the welding exceeded the Zn melting temperature. The melted Zn was mixed with Al who was in plastic flow state, and the Zn diffused and dissolved into the Al matrix to form metallurgical joint. The highest tensile shear strength of the joints was 7.3 k N.When welded the Al/Zn/Cu joint configuration using Cu as upper plate with pinless tool, macro groove defects were found on the joints because of insufficient material flow and heat input which was rised by unreasonable welding parameters. “Onion rings” structure was also found under the pinless tool shoulder in the Cu matrix. The “onion rings” structure was different from the tranditional one, which was like oblate “onion rings”. The tranverse section showed cresent-like structure because of the softening of the metal caused by the temperature increasing. With the process of mixing, diffusion, and dissolving, the interlayres showed double-layer structure. The highest tensile shear strength was 8.9 k N. Two different alloys were found on the fracture surface. The fracture mode was intercrystalline fracture.