Thermal treatment effect on the mechanical properties of 1570, 1580 and 1590 aluminum alloys

The study addresses the effect of thermal treatment on the mechanical properties and grain size of magnesium rich alloys with small scandium additions 1570, 1580 and 1590. The effect of preheat temperature (within 260…440 °С range) and soaking time (within 2 – 100 hours range) on yield strength, tensile strength and relative elongation of the alloys under investigation  was analyzed. Mechanical properties were determined using uniaxial tensile tests in accordance with ISO 6892-1. In addition, for some modes the microstructure was studied for Al3Mg2 β-phase presence and distribution by optical metallography methods depending on thermal treatment conditions. The studies demonstrated that supersaturated solid solution in the 1570 alloy decomposes faster in the entire studied temperature range, and after 48 hours soaking, its strength properties start degrading. At the same time, the 1580 and 1590 alloys are much more thermally stable, with slightly lower yield strength after long soaking time, while tensile strength remains unchanged. The conditions of 260 °C annealing temperature are not favorable for plastic properties, severely degrading (due to β-phase formation) in the 1570 and 1580 alloys. Plastic properties degradation is not so evident at higher soaking temperature, however, the 1590 alloy maintains the highest plasticity indices.