Study on Mg/Al Weld Seam Based on Zn-Mg-Al Ternary Alloy.

Liming Liu,Meili Zhu,Fei Liu

doi:10.3390/ma7021173

Abstract

Based on the idea of alloying welding seams, a series of Zn–xAl filler metals was calculated and designed for joining Mg/Al dissimilar metals by gas tungsten arc (GTA) welding. An infrared thermography system was used to measure the temperature of the welding pool during the welding process to investigate the solidification process. It was found that the mechanical properties of the welded joints were improved with the increasing of the Al content in the Zn–xAl filler metals, and when Zn–30Al was used as the filler metal, the ultimate tensile strength could reach a maximum of 120 MPa. The reason for the average tensile strength of the joint increasing was that the weak zone of the joint using Zn–30Al filler metal was generated primarily by α-Al instead of MgZn2. When Zn–40Al was used as the filler metal, a new transition zone, about 20 μm-wide, appeared in the edge of the fusion zone near the Mg base metal. Due to the transition zones consisting of MgZn2- and Al-based solid solution, the mechanical property of the joints was deteriorated.

Highlights

It has been well known that Al alloys have attractive mechanical and metallurgical properties, including high strength and excellent corrosion resistance, and they are widely used for structural components in many applications, such as aerospace, automobiles and the electronics industry [1,2].Due to Mg alloys’ unique properties, such as a lower weight ratio and electromagnetic shielding capability [3,4], they will have great potential uses in the manufacturing industry
The MZAS with excellent plasticity has been reported by Straumal et al [16], owing to the fact that the Al–Zn and Al–Mg systems are the basis of multicomponent alloys, which present a high strain-rate superplasticity, and having observed the wetting of grain boundaries for these systems, it is suggested that grain boundary pre-melting or pre-wetting is responsible for the high strain-rate superplasticity
Zn–30Al filler metal is used as an example to estimate the solidification time of the welding pool

Summary

Introduction

It has been well known that Al alloys have attractive mechanical and metallurgical properties, including high strength and excellent corrosion resistance, and they are widely used for structural components in many applications, such as aerospace, automobiles and the electronics industry [1,2]. Previous research has indicated that the formation of Mg–Al intermetallic compounds (IMCs) could be avoided by filling Zn metal in the weld seam in the gas tungsten arc (GTA) welding of Mg and Al alloys [15]. The MZAS with excellent plasticity has been reported by Straumal et al [16], owing to the fact that the Al–Zn and Al–Mg systems are the basis of multicomponent alloys, which present a high strain-rate superplasticity, and having observed the wetting of grain boundaries for these systems, it is suggested that grain boundary pre-melting or pre-wetting is responsible for the high strain-rate superplasticity This explained why the tensile strength of the Mg/Al joint with Zn filler metal was increased compared with the Mg/Al direct fusion joint. The mechanical properties and the fracture mechanisms of the joints will be discussed

Experimental Materials and Instruments

The Design of Zn–xAl Filler Metals

Analysis of the Weld Pool Solidification

Microstructure of the Welded Joints

Tensile Strengths and Fractures of the Welded Joints

Conclusions