The Influence of Grain Boundary Wetting on the Mechanical Properties of AMg6 Polycrystals

In this paper, the grain boundary wetting phase transition in an aluminum-based AMg6 alloy is studied. The transition from incomplete wetting of grain boundaries to complete one occurs in the temperature range from 555 to 590°C. Below 555°C, the melt enriched in magnesium forms separate lenticular droplets at the grain boundaries. Above 590°C, the magnesium-enriched melt forms continuous layers along almost all boundaries between aluminum grains and, thus, forms a kind of shell or shell around each grain of the matrix. During quenching after annealing, the grain boundary layers enriched in magnesium solidify. Previously, we observed that such grain-boundary shells made of the second phase can significantly change, for example, the electrical or magnetic properties of a polycrystal. In this paper, we found for the first time that a change in the fraction of completely wetted boundaries can also affect the mechanical properties of the material (after quenching). In particular, in samples annealed at 550°C or below, when there are no completely wetted boundaries, the conditional yield strength σ0.2 almost does not change. Starting from 550°C, as the fraction of completely wetted boundaries increases, the value of σ0.2 drops rapidly and decreases by about one and a half times by 600°C. At the same time, the Young modulus, which is determined mainly by the bulk properties of aluminum grains, remains virtually unchanged with increasing temperature and a change in the fraction of completely wetted boundaries. Thus, the physical effect we have discovered provides materials scientists with a fundamentally new tool for purposefully changing the mechanical properties of various polycrystalline materials.