Improvement of the Laser-Welded Lap Joint of Dissimilar Mg Alloy and Cu by Incorporation of a Zn Interlayer

During pulsed laser welding of AZ 31B magnesium (Mg) alloy and T2 pure copper (Cu), Cu2Mg and Mg2Cu are generated, but the bonding ability of the two compounds is usually weak, resulting in low strength. In order to improve the joint of two dissimilar metals, a zinc interlayer was inserted between the Mg alloy and Cu, and the effects of the thickness of the Zn interlayer on the microstructure and properties of the joint were studied. The fused zone consisted of Cu2Mg and MgZn, and, according to first-principles calculation, in the same energy range, the area enclosed by the density of the state curve of MgZn was larger than that of Cu2Mg. Hence, the bonding ability of MgZn was better than that of Cu2Mg, and MgZn improved the strength of the welded joint. The most advantageous thickness of the Zn interlayer was 0.1 mm, and the shear strength was 48.15 MPa that was 161% higher than that of the directly welded Mg/Cu joint.

Characterization of Influences of Steel-Aluminum Dissimilar Joints with Intermediate Zinc Layer

Brittle intermetallic phases are formed when steel and aluminum are joined. Therefore, it is difficult to use this combination of materials when applying the multimaterial design in the construction of load-adapted and weight-adapted structures. In order to largely avoid the formation of these brittle phases, joining processes based on diffusion processes, such as composite forging, depict a good solution approach. The materials are joined in a solid state. Furthermore, zinc additives are used to create the joint. Zinc forms a compound with both steel and aluminum without the formation of brittle phases. By combining the composite forging process with zinc additives, strength values of 26 N/mm2 can be reached. This is higher, in comparison to former investigations of resistance spot welded and clinched joints. The joint properties depend on the composition of the zinc interlayer. Small amounts of magnesium in the zinc interlayer affected the strength and ductility values. While the strength decreased by about 30% in contrast to the zinc layer without magnesium, the ductility increased by 60%. This effect was probably due to the metallurgical impact of the alloying elements on phase formation, as could be shown by energy dispersive X-ray spectroscopy (EDX) analyses of the joint zones. Thereby, it was shown that the brittle intermetallic phases are located only in small areas.