UC San Diego

Mechanical processing improves the mechanical behavior of modern materials, thus increasing their strength, toughness, and other physical properties. This research focuses on the mechanical properties of magnesium alloy WE43 under conditions of severe plastic deformation. The main objective of this research is to characterize structurally the magnesium alloy and analyze the formation of bulk ultrafine grains produced by two main techniques which promote the change in grain size and consequently the increase of the mechanical strength. Multi Directional Forging is a compression procedure applied to the material in all three directions, maintaining the dimensional ratio and increasing the strain produced until the cumulative strain be greater than 2.0. This was conducted at 550 °C. As magnesium alloy WE43 has good properties at higher temperatures; the cumulative plastic strain obtained was higher than 2.0. To complement the study of the strength increase via plastic deformation, Equal Channel Angular Processing was applied at three different temperatures. The required stress to push the material through the die at 550 °C was 867 MPa. The results show a moderate decrease in grain size from 18 µm to 14 µm in ECAP and 12 µm in Multi Directional Forging. This decrease in grain size results in an increase in the hardness. In view of the brittleness of the magnesium alloy it was not possible to increase the plastic strain as expected in Multi Directional Forging per pass; the samples fractured if the stress was increased beyond 230 MPa. The yield stress at 1.6 x 10-2 s-1 increased from 87 MPa for the initial condition, to 115 MPa for the specimens subjected to a strained. In dynamic compression test, experiments were conducted at a strain rate of 2.5x103 s-1 and the yield stress increased to 246 MPa. This shows that magnesium has a high strain-rate sensitivity.