Weldments aluminum alloys

Corrosion resistance of aluminum alloys. Researchers have shown that aluminum alloys, both welded and unwelded, have good resistance to uninhibited HN03 (both red and white) up to 50°C. Above this temperature, most aluminum alloys exhibit knife-line attack (a very thin region of corrosion) adjacent to the welds. In inhibited fuming HNO3 containing at least 0.1% hydrofluoric acid (HF), no knife-line attack was observed for any commercial aluminum alloy or weldment even at 70°C (160°F). 

W.W. Sanders, Jr. and F.V. Lawrence, Jr., Fatigue Behavior of Aluminum Alloy Weldments, STP 648, American Society for Testing and Materials, 1978, p 22... 

THE FATIGUE PROPERTIES OF ALUMINUM ALLOY 5083-H113 PLATE AND BUTT WELDMENTS AT 75° AND -300°F... 

Galvanic Effects. The resistaiice to corrosion of weldments in aluminum alloys is affected by the alloy being welded and by die filler alloy and welding process used. Galvanic cells that cause corrosion can be created because of corrosion potential differences among the base (parent) metal, the filler metal, and the heat-affected regions where microstructurai changes have been produced. 

The variations in corrosion potential (equilibrium potential) across three welds are shown in Figure 11.7 for Alloys 5456 and 2219. These differences can lead to localized corrosion. In general, the welding procedure that puts the least amount of heat into the metal has the least influence on micro-structure and the least chance of reducing the corrosion behavior of aluminum weldments. 

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