Temperature dependency of mechanical behavior and strain rate sensitivity of an Al-Mg alloy with bimodal grain size

An Al 5083 alloy with an ultrafine grained/coarse grained bimodal has been shown to exhibit greatly improved strength when compared to conventional Al alloys. Its properties have also been observed to be sensitive to strain rate, anisotropy, and coarse grain ratio. This work studies how temperature affects this material's properties, as well as how it modifies the effects of the previously studied parameters, through uniaxial tensile tests at temperatures up to 473 K (200 °C) and microscopic examination of the specimens and their failure surfaces. It was found that the strength of the material decreased rapidly with increasing temperature such that at the highest test temperature, the bimodal material actually exhibited lower strength than conventional Al 5083 at the same temperature. No significant grain growth due to temperature effects was observed. The strain rate sensitivity exponent was found to have a non-monotonic dependence on temperature with negative values at room temperature which increased to positive value at 383 K (110 °C) and decreased to a negative value again at 473 K (200 °C). Anisotropic effects were noted both in the material's properties and in the texture of its fracture surface. Dynamic recovery was observed in the higher temperature tests and the amount of recovery was found to be affected by the material's coarse grain ratio.