AN INVESTIGATION OF THE EFFECT OF VARIOUS HEAT TREATMENTS ON THE CORROSION RESISTANCE OF A HIGH- STRENGTH ALUMINUM-COPPER CASTING ALLOY

摘要

The AA 206 family of aluminum casting alloys includes some of the strongest, toughest aluminum foundry alloys in current use. Since they also have excellent low cycle fatigue strength, they could potentially be used in a number of automotive applications, e.g. suspension, to reduce vehicle weight. However, the tendency to hot shortness (tearing) had until recently held back the alloys' development. New formulations, with improved grain refining and reduced susceptibility to hot tearing, have renewed interest in using the alloys in automotive applications. Heat treatments required to produce the desired mechanical properties can lead to the alloy becoming susceptible to SCC (Stress Corrosion Cracking) and/or intergranular corrosion. In this study, a cast B206 alloy has been subjected to a series of heat treatments involving a 3-step solution treatment + both natural and artificial aging. The corrosion resistance has been primarily determined using potentiodynamic testing and associated metallography. The potentiodynamic corrosion testing results are compared with our earlier data on immersion corrosion testing and elongation values from mechanical testing. Heat treatment schedules that give materials resistant to intergranular corrosion in the immersion testing, also generally give higher levels of corrosion and elongation values below the required level.