The welding of aluminium and its alloys

Welding metallurgy

Introduction

Ideally a weldment - by this is meant the complete joint comprising the weld metal, heat affected zones (HAZ) and the adjacent parent metal - should have the same properties as the parent metal. There are, however, a number of problems associated with the welding of aluminium and its alloys that make it difficult to achieve this ideal. The features and defects that may con­tribute to the loss of properties comprise the following:

• Gas porosity.

• Oxide inclusions and oxide filming.

• Solidification (hot) cracking or hot tearing.

• Reduced strength in the weld and HAZ.

• Lack of fusion.

• Reduced corrosion resistance.

• Reduced electrical resistance.

This chapter deals with the first four of these problem areas, i. e. those of porosity, oxide film removal, hot cracking and a loss of strength. Before dis­cussing these problems, however, there is a brief introduction as to how metals achieve their mechanical properties. Some of the terms used to describe specific parts of a welded joint are shown in Fig. 2.1.