Metallurgical Parameters Determining T4 and T6 Treatment Behavior of A413.1 Base Alloys

The A413.1 aluminum alloy is known for its excellent fluidity, corrosion resistance and good mechanical properties which make it an ideal candidate for complex shapes and thin-walled castings. This alloy is commonly used in automotive components, housings and general industrial applications. The microstructure of A413.1 alloys comprises several intermetallic phases; however, only the β-Al₅FeSi phase influences the size of the eutectic silicon particles. These compounds solidify first and carry with them a certain quantity of strontium which remains near these compounds to more significantly modify the surrounding eutectic silicon particles. The other intermetallic phases do not affect the morphology of the eutectic silicon particles. The addition of strontium only and strontium together with magnesium improves the ultimate strength of as-cast alloys while the addition of silver and zinc improves the yield strength. After a T4 heat treatment, it is the base alloy—with an addition of strontium and copper—that obtains the highest tensile strength values. Dissolving for twenty-four hours does not improve the strength of the alloys compared to dissolving for four hours. For T6 heat treatments, aging at 155 °C is more appropriate for alloys not containing copper, and aging at 180 °C increases the properties of alloys which do contain it. On the other hand, the aging temperature of 240 °C is too high to be applied for five hours as it produces overaging. Aging at a temperature of 180 °C considerably reduces the ductility of the alloys. In this case, many of the tensile bars are fractured in the elastic region. The study was supported by the use of quality index charts. About 1200 tensile test bars were pulled to fracture during the course of these investigations.