Al-Mg合金の高温における延性低下

抄録

The dependence of the hot ductility of Al-Mg solid solution on temperature, strain rate, grain size and solute content has been examined in detail by use of tensile test. At a constant strain rate, a ductility (reduction of area) versus temperature curve showed a remarkable trough. With increase in the strain rate, the ductility trough appeared at higher temperatures, while its depth remained almost constant. The temperature at which ductility becomes minimum (T_min) can be correlated with the strain rate (\dotε) by \dotε∝exp(−Q_φ⁄RT_min), where Q_φ (137 kJ/mol) agrees well with the activation energy for volume diffusion. The ductility is determined uniquely by a parameter Z=\dotεexp(Q_φ⁄RT), where R is the gas constant and T the absolute temperature. The effect of the grain size on the minimum ductility (φ_min) at a constant strain rate, can be empirically expressed as φ_min=1⁄(1+d⁄D₀), where D₀ is a materials constant and increases with increasing solute content. The ductility loss was associated with the intergranular fracture, and a number of small dimples were observed on the fracture surface, suggesting the growth and interlinkage of cavities. The results are compared with those for other metallic materials.