A New Theoretical Approach Based on the Maxwell Model to Obtain Rheological Properties of Solidifying Alloys and Its Validation

This paper proposes a new method for obtaining the rheological properties of solidifying alloys in the brittle temperature range (BTR). In that range, alloys show not only rheological, but also brittle behavior. Conventional methods to obtain rheological properties require steady state stress with ductility. Therefore, rheological properties of BTR alloys are unobtainable, or are otherwise including the effects of microscopic damage. The method proposed in this paper uses the stress–strain relation derived from the Maxwell model assuming that strain hardening is negligible in solid-liquid coexistence states. By removing the plastic strain term, the creep strain rate in Norton’s law is derived by the total strain rate and stress rate without the steady state stress condition. Consequently, the stress exponent n and material constant A of Norton’s law can be obtained even for alloys in the BTR. We applied this method to both tensile process before crack initiation and stress relaxation process. According to the Maxwell model, couples of the properties (n and A) obtained in both processes must be equal. Therefore, the difference can validate the obtained properties. From tensile and stress relaxation tests, we obtained the properties of solidifying Al-5 wt pct Mg alloy. We validated results by examining the difference. This report is the first to provide a method to obtain the rheological properties of BTR alloy without damage.