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 similar to 320 degrees C is caused by precipitation of the Al3Sc particles. The cold-rolling prior to a heat treatment has no substantial effect on temperature position of the Al3Sc-phase precipitation. The formation of Al6Mn and/or Al-6(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 Al3Sc particles was determined.