Sammendrag
The weldability of the 7108 aluminum extrusion alloy has been found to exhibit a high sensitivity to iron impurity content. This is believed to be related to the formation of a high-melting-temperature Al-Fe eutectic, capable of blocking interdendritic fluid flow and impeding the feeding of solidification shrinkage and thermal strain. Other high-temperature, eutectic-forming impurities have been found to behave in a similar manner when added to Alloy 7108 in a controlled manner. The circular patch test (CPT) was adapted to evaluate the effect of impurity elements on the solidification cracking susceptibility of welds made on cast 7108 coupons, treated with different impurity metal additions. Results from the CPT have shown a correlation between the amount of eutectic generated, as predicted using the Scheil Equation, and the susceptibility to cracking. However, in some instances, impurities are also observed to refine the grain size, an effect that tends to counteract their negative influence on weldability.
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