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.

The welding of aluminium and its alloys

Alloy designations: wrought products

Table A.4 BS EN BS EN Old BS/DTD Temperature (°C) numerical chemical number designation designation Liquidus Solidus IVIdUng range Al 99.99 1 660 660 0 AW-1080A Al 99.8 1A AW-1070A …

Principal alloy designations: cast products

Table A.3 BS EN numerical designation BS EN chemical designation Old BS number ANSI designation Temperature (°C) Liquidus Solidus Melting range Al 99.5 LM0 640 658 18 AC-46100 Al Si10Cu2Fe …

Physical, mechanical and chemical properties at 20°C

Table A.2 Property Aluminium Iron Nickel Copper Titanium Crystal structure FCC BCC FCC FCC HCP Density (gm/cm3) 2.7 7.85 8.9 8.93 4.5 Melting point (°C) 660 1536 1455 1083 1670 …

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