Discontinuous Deformation of Al-Mg Alloys

Effects of the solute concentration and the grain size on the discontinuous deformation of Al-Mg alloys have been studied based on a new idea which differs somewhat from the conventional static strain aging model. The concentration of Mg and the grain size were varied from 0.2 to 2.5 mass% and from 40 to 500 μm, respectively. Tensile tests were performed in the temperature range from 243 to 473 K. For discussion about effects of the solute concentration and the grain size, only the temperature of 273 K was used. The exponent M corresponds to so-called (m+β), obtained from the relationship between the critical strain and the strain rate, depends on both of the solute concentration and the grain size. The value of M increases with increasing Mg concentration. The increasing value of M with the solute concentration was discussed based on the assumption that deformation-induced vacancies depend on the plastic strain. The value of M=1.0 was obtained when the Mg concentration was extrapolated to zero. The relation between εc and C0 can be expressed as εcM∝C0−3, this relation cannot be explained using the t2⁄3 rule proposed by Cottrell-Bilby. It can be explained well provided the experimentally accepted t1⁄3 rule is allowed. The activation energy of discontinuous deformation on the low temperature side was determined as 47.1 and 47.9 kJ/mol for Al-0.5 and 2.5 mass%Mg alloys, respectively.