Influence of Welding Speed on Characteristics of Non-Axisymmetric Laser-Tungsten Inert Gas Hybrid Welded Mg/Al Lap Joints with Zn Filler.

Xinze Lv,Hongyang Wang,Liming Liu

doi:10.3390/ma13173789

Abstract

A non-axisymmetric laser-tungsten inert gas (TIG) heat source was designed to join Mg–Al dissimilar metals with pure Zn filler at a series of welding speeds (500–900 mm/min). Laser and TIG heat sources respectively acted on Al and Mg base metals to precisely control their dissolution into the welding pool. The solidification rate of liquid metal was controlled by adjusting the welding speed, then the reaction process of Mg, Al and Zn could be accurately regulated. The results indicated that various microstructures including Al solid solution, Zn solid solution, Mg–Zn intermetallic compounds (IMCs) and eutectic structure formed in the joint produced at different speeds. Lower welding speed (500 mm/min) caused the microstructure coarsening and higher welding speed (900 mm/min) would lead to the enrichment of MgZn2 intermetallic compounds. At the optimal welding speed of 800 mm/min in particular, fine MgZn2 IMCs grains uniformly distributed in the Al and Zn solid solution. The tensile-shear load reached a maximum of 1052.5 N/cm and the joint fractured at the fusion zone near the Al base metal.

Highlights

Al alloy, as the most widely used non-ferrous metal, has a lot of attractive properties such as low density, high specific strength, excellent corrosion resistance and good formability
Friction stir welding (FSW) [3,4,5,6,7,8], resistance spot welding (RSW) [9], contact-reaction brazing [10,11,12], ultrasonic spot welding [13,14,15] and explosive welding [16,17,18] were employed for joining Mg–Al dissimilar metals, and the formation of intermetallic compounds (IMCs) was restrained by reducing the reaction temperature and reaction time of the liquid metal
Decreasing the heat input could not completely eliminate the brittle IMCs in the joint. Some alloying elements such as Zn11 + (Zn), Cd, Cu, Fe, Ni, Zr and Ti were added into the weld [19,20,21,22,23,24,25], the brittle Mg–Al IMCs were replaced by other compounds with low brittleness [26]

Summary

Introduction

As the most widely used non-ferrous metal, has a lot of attractive properties such as low density, high specific strength, excellent corrosion resistance and good formability. Mg alloy, which is the lightest structural metal, possesses many unique features including light weight, excellent damping capacity and electromagnetic shielding performance. Both of Mg alloy and Al alloy are widely applied in automobiles, aerospace and electronic industries for weight reduction [1,2]. The joining of Mg–Al dissimilar metals is extremely difficult, since a large amount of brittle. Mg–Al intermetallic compounds (IMCs) form during the welding process, and distribute continuously in layers. This difficulty can be solved by two methods, adopting solid-state bonding process or alloying the weld seam. Some alloying elements such as Zn, Cd, Cu, Fe, Ni, Zr and Ti were added into the weld [19,20,21,22,23,24,25], the brittle Mg–Al IMCs were replaced by other compounds with low brittleness [26]

Methods

Results

Conclusion