Phase transformations in non-isothermally annealed as-cast and cold-rolled AlMnScZr alloys

The effect of Mn addition on the microstructure, thermal and mechanical properties in as-cast and cold-rolled Al–Sc–Zr alloys was studied. Electrical resistometry, differential scanning calorimetry and microhardness measurements were used. Transmission electron microscopy, electron backscatter diffraction and X-ray diffraction of specimens quenched from temperatures of pronounced changes in resistivity helped to identify the microstructural processes responsible for resistivity changes. The distinct microhardness increase observed after annealing above ∼320°C is caused by precipitation of the Al Sc particles. The cold-rolling prior to a heat treatment has no substantial effect on temperature position of the Al Sc-phase precipitation. The formation of Al Mn and/or Al (Mn,Fe) particles is responsible for the intensive resistivity decrease of the cold-rolled materials compared to the as-cast materials. Precipitation of these particles has an insignificant effect on microhardness. The apparent activation energy for the precipitation of the Al Sc particles was determined.