The Paint Bake Intervention: The Effect of Paint Bake Treatment on Al-Fe (Zn, Mg) Alloy Castings for Structural Automotive Application

The Al-Fe-based eutectic alloy featuring Zn and Mg as precipitation strengtheners was used to manufacture test plates using high-vacuum high-pressure die casting (HVHPDC). The castings have previously exhibited natural ageing with mechanical properties rising to meet up with the industry benchmark within 3 days of natural ageing in the as-cast condition. Attempting to mimic the industrial process to which some of this alloy will be deployed, some samples were given “paint bake” treatment which is typical on a coating line where the structural parts are heated to 120–200 °C for 30 minutes. The samples were treated at various ages and results obtained. It was deductible that samples of different ages react in different ways to the “paint bake” treatment. Generally, the strength of the samples would decrease upon treatment and then increase to equalize with the values of the non-paint-baked samples. However, there were different strengthening rates; some remained “dead” in the low mechanical properties state or rising very slowly to catch up with the natural ageing curve for the duration of the experiment. Samples treated at stages when the precipitates are very actively clustering or dissolving showed the worst results suggesting that it may not be a good time to disrupt the NA process.