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Understanding the role of the slip systems and their evolution with temperature is critical to the correct simulation of the mechanical behavior of magnesium alloys. In this paper, relations are proposed for evolution of the CRSS values of different slip systems and strain-rate sensitivity factor, stating them as functions of temperature and strain-rate. These relations are used in conjunction with the Crystal Plasticity Finite Element (CPFE) model for prediction of stress-strain curves and r-values at elevated temperatures (75°C to 250°C). The new relations can predict the decrease in stress level, the anisotropy of the material, and the decrease in the difference between the r-values in the RD and the TD with the increase in temperature. The results confirm the trends predicted with Taylor-type and VPSC models. In particular, they confirm the high activity of the slip systems at higher temperatures.

The deformation characteristics of a commercial AZ31 magnesium sheet alloy were investigated at elevated temperatures. Tensile experiments were conducted at temperatures 300°C, 400°C and 450°C and at strain rates, 0.001s-1, 0.01s-1 and 0.1s-1. Depending on the test temperature, fracture analysis of failed specimens revealed three different types of failure: (1) by moderate necking, (2) by interlinkage cavity, (3) by strong necking. Plastic strain ratios, r-values were derived from the strain ratios of width and thickness of the fractured tensile specimens. The r-value increased with increasing temperature and strain rate.

Tempered martensite assisted steels are of recent research interest for good strength and ductility combination. This paper discusses the effect of tempered martensite volume fraction on the final properties of cold rolled and subcritically annealed Al containing TRIP steel. The samples were TRIP annealed and the retained austenite volume fraction was measured using X-ray diffraction technique. The steel samples were subsequently cold rolled to obtain strain induced martensite, deformed ferrite and bainite in the microstructure. The final tempered martensite volume fraction corresponds to the initial retained austenite volume fraction of the steel. The cold rolled TRIP steel samples were subsequently subcritically annealed at 500°C for 1 hour to obtain tempered martensite, fine ferrite and bainite. Shear Punch testing was used to evaluate the mechanical properties. The properties are analyzed and the results are discussed.

The TRansformation Induced Plasticity (TRIP) phenomenon in low alloy multiphase steels has been investigated as a mechanism to improve strength and ductility. Most characterization studies performed to date on TRIP steels consider only quasi-static tensile loading, although stress-state and strain-rate are known to affect the martensitic transformation. In this paper, quasi-static and dynamic tests are performed in tension and compression to evaluate the mechanical response as well as to determine the role of strain-rate on the amount of retained austenite. The results indicate a differential response between compression and tension and show considerable rate dependency for the low alloy TRIP steel.

The high strain rate deformation behavior of commercially available dual phase steel was studied by means of split Hopkinson bar apparatus in shear punch mode with an emphasis on the influence of microstructure. The cold rolled sheet material was subjected to a variety of heat treatment conditions to produce several different microstructures. Dual phase microstructures with different fractions of martensite were obtained by changing intercritical annealing temperature and time. Various microstructures of ferrite plus pearlite, or acicular ferrite/bainite, or bainite and martensite/carbide were obtained by changing the cooling rate after annealing. The effects of low temperature tempering and bake hardening treatment were also investigated for some selected specimens.

The evolution of microstructure in a Mg 3.4%AI-0.16%Zn-0.33%Mn alloy tube was studied during deformation by ring hoop tension testing (RHTT). When the tests were carried out at moderate temperatures and relatively high strain rates, the accompanying c-axis strains were mainly accommodated by twin formation. At temperatures above 200°C and the lowest strain rate (0.001s-1), the formation of voids in the partially dynamically recrystallized regions caused premature fracture. The microstructural development in hot gasformed samples was similar to that observed during RHTT testing. These results indicate that RHTT testing is an effective way of studying the deformation behavior of Mg alloys during tube gas forming.