Effects of Germanium, Copper, and Silver Substitutions on Hardness and Microstructure in Lean Al-Mg-Si Alloys

It is shown that strength loss in a 6060 Al-Mg-Si alloy caused by reduction in solute can be compensated by adding back smaller quantities of Ag, Ge, and Cu. Nine alloys were investigated. Ge was found to be the most effective addition, strongly refining the precipitation. The hardness is discussed in terms of statistics of the precipitates near a T6 condition, as acquired by transmission electron microscopy (TEM). Precipitates in some conditions were also investigated by high-angle annular dark-field scanning TEM. The added elements have strong influence on the main hardening precipitate, beta aEuro(3), changing its structure and promoting disorder.