Metal Processing Institute
Advanced Casting Research Center

Research Programs

Yield Stress Measurements and Microstructure Evolution in SSM Al-Based Alloys


Research Team:

Qingyue Pan
Diran Apelian

Introduction

Semi-solid metal slurry is a mixture of liquid metal and solid particles. The solid particles have predominantly a globular shape during the reheating stage. In essence, the rheological behavior of semisolid metal slurry is similar to that of visco-plastic materials such as concentrated suspensions, pastes, foodstuffs, emulsions and foams. This class of materials is characterized by the existence of a yield stress, which implies the material behaves as a "solid" if the applied stress is below the yield stress; if the applied stress exceeds the yield stress, however, the material will flow and show liquid-like behavior. Yield stress of semi-solid metals has a significant effect on its filling behavior during semi-solid forming, and needs to be determined experimentally.

Objectives

The aim of this project was to establish yield stress vs. temperature/fraction solid relationship for various commercial semi-solid aluminum alloys. Experimental data have been provided to the modeling team and also utilized to optimize industrial practice. In this project, a new methodology was developed for yield stress measurement of semi-solid slurry at different processing conditions. In addition, quantitative image analysis was conducted to characterize microstructure evolution of semisolid alloys in the two-phase region, and thus to reveal its effect on flow/yielding behavior.

Salient Results

Figures 1 and 2 give the yield stress measurement results of A356 and 357 alloys as a function of temperature. Figures 3 and 4 give the yield stress measurement results of A356 and 357 alloys as a function of fraction solid. Figure 5 compares yield stress values of commercial A356 billets as a function of processing method and temperature. From Figures 1 through 5, one can see that:

SSM Related Publications

Related Publications

Figure 1: Yield stress of GR A356 and MHDA356 alloys as a function of temperature.

Figure 2: Yield stress of GR A356 and MHDA356 alloys as a function of temperature.

Figure 3: Yield stress of GR A356 and MHD A356 alloys as a function of solid fraction.

Figure 4: Yield stress of GR 357 and MHD 357 alloys as a function of solid fraction.

Figure 5: Yield stress of commercial A356 billets as a function of processing method and temperature.

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Last modified: October 15, 2007 11:46:20