Endurecimento por precipitação em função das condições de solidificação em ligas leves de Al-Zn-Mg com variações no teor de zinco

Abstract

The objective of the present work is to develop two modified ternary Al-Zn-Mg alloys, with Zn content about 5wt% and 8wt%, and to evaluate the precipitation hardening (solutioning and artificial ageing – T6) as a function of solidification conditions. The 752 (Al-5%Zn-2%Mg) and 782 (Al-8%Zn-2%Mg) alloys were obtained to analyze the influence of Zn content, as well as the relationship between solidification conditions, precipitation hardening, and mechanical properties before and after heat treatments. Unidirectional vertical upward solidification was performed in a metallic mold cooled by water in the bottom and instrumented using thermocouples to obtain the ingots. Samples extracted from ingots were metallography characterized by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and the mechanical properties were determined by hardness, microhardness, tensile and wear testing. The results showed that the increase of 3% of zinc in the chemical composition improved the hardness of 44%, the superficial wear of 27.7% and the tensile strength of 31.5% (in T6 condition). When comparing the results against data from some similar wrought alloys, it is concluded that the as-cast and heat treated 782 alloy can replace those, according to design specifications.