Processing, microstructure and superplasticity in Al-Mg-Mn alloys

Abstract

A thermomechanical processing (TMP) schedule developed in previous work was modified to provide for an increasing strain and strain rate with each polling pass. three alloys, Al-10mg, Al-10mg-0.2Mn, and AL-10mg-0.5mn (compositions in wt. pct.), were processed utilizing this schedule. Samples were obtained following various rolling passes for subsequent microscopy analysis. Materials in both the as-rolled condition and following 25 minutes of annealing were studied. Utilizing backscattered imaging techniques with the scanning electron microscope, the microstructural evolution of these alloys during the TMP were studied. Second phase particles were observed to precipitate on grain boundaries and deformation structures in the intermediate stages of the TMP. In addition, second phase precipitates developed on MnAl6 particles through heterogeneous nucleation in the Manganese containing alloys. Particle simulation of recrystallization was observed in the latter stages of the TMP as precipitate particles coarsened. Tensile testing at 300(o)C demonstrated the superplastic response of each alloy, and showed that the addition of Manganese enhances superplastic response. Strain rate sensitivity coefficients were observed to initially decease with increasing strain, but then increased with further straining.