Comparison of the features of the formation of joints of aluminum alloy 7075 (Al-Zn-Mg-Cu) by laser, microplasma, and laser-microplasma welding

Volodymyr Korzhyk,Yuhui Yao,Volodymyr Shcheretskiy,Nataliia Fialko,Andrii Grynyuk,Yevhenii Illiashenko,Sviatoslav Peleshenko,Viktor Kvasnytskyi,Vladyslav Khaskin,Olena Berdnikova

doi:10.15587/1729-4061.2022.253378

Abstract

This paper reports a study into features of the formation of structures of permanent butt joints of plates with a thickness of 1.5 mm made from the high-strength aluminum alloy 7075 of the Al-Zn-Mg-Cu system. Welding by melting these joints was performed using three techniques: laser, microplasma, and hybrid laser-microplasma. To implement the latter two, a compressed arc on a multipolar asymmetric current was used. The purpose of the research was to establish the tendency to the formation of characteristic defects and the possibility of their elimination. It has been determined that during laser welding a small (~5 %) volumetric fraction of defects in the form of pores is formed, residual welding deformations are minimized. There is a decrease in the hardness of the melted metal by 15 % with a simultaneous increase in the hardness of the heat-affected zone (HAZ) by 8...12 % relative to the base metal. In the melted metal, cavities up to 100 μm in size are formed, which are the center of the origin of hot cracks with a length of 25‒30 μm. There are oxide inclusions in the root part of the seam. With microplasma welding, the volume fraction of defects of the melted metal in the form of pores with a size of 10...105 μm increases (up to 25 %). The hardness of the melted metal is reduced by 30 % with the hardness of the HAZ metal close to the base metal. In laser-microplasma welding, the volumetric fraction of defects of the melted metal in the form of pores with a size of 15...25 μm is reduced to 5 %. The hardness of the melted metal is reduced by 15...20 % with the hardness of the HAZ metal close to the base metal. In the lower part of the melted metal, cavities of ~100 μm are formed. No microcracks were found in the seam metal. Analysis of the research results showed the advantage of the laser-microplasma technique. This method reduces the use of laser energy by 40...50 %, the lifetime of the welding pool (0.03...0.05 s) approaches laser welding, it eliminates the danger of burnout of alloying elements.

Highlights

Aluminum alloys are widely used in modern industry for the manufacture of lightweight structures with high strength and corrosion resistance
It is established that laser welding of butt joints of aluminum alloy 7075 makes it possible to obtain sufficiently narrow seams with minimal costs of li near energy (5 J/mm) and the time of existence of the melt bath (0.02...0.04 s)
The granularity of the compound is regu lar, the grains are equiaxial in the melted metal and elonga ted along the fusion line ( = 2...3) and in heat-affected zone (HAZ) ( = 2.5...5)

Summary

Introduction

Aluminum alloys are widely used in modern industry for the manufacture of lightweight structures with high strength and corrosion resistance. Materials Science execute high-quality non-detachable joints [2]. For this purpose, various welding techniques are used [3]. In the manufacture of those structures, of particular interest is the possibility of using high-strength aluminum alloys Such alloys make it possible to create lightweight structures with increased mechanical properties, which makes their use in modern industry relevant. Among the high-strength aluminum alloys, the most interesting are the alloys of the Al-Zn-Mg-Cu system (7xxx series), which have the highest mechanical properties Welding such alloys is difficult due to their tendency to form hot cracks and pores. Studies of structure formation during welding of thin-walled joints from these alloys using concentrated energy sources are relevant

Literature review and problem statement

The aim and objectives of the study

The study materials and methods

Findings

Conclusions