Effect of plastic deformation on microstructure and thermoelectric properties of Mg_(2)Sn alloys

In the present work,the effect of deformation on microstructure and thermoelectric properties of Mg 2 Sn alloys having excess magnesium concentrations is examined.The cast alloys were prepared using radio-frequency(RF)induction melting under an argon atmosphere.These alloys were thermo-mechanically processed via compression at different temperatures to various true strains.At room temperature,the alloys failed at a true strain of∼13%.However,at elevated temperatures,the alloys were observed to be highly plastic.For alloys compressed at 673 K to a true strain of 1,a prominent substructure formed.The subgrain size was∼3-5μm.It is believed that the substructure arose from the action of dynamic recovery.Following deformation,the thermoelectric performance of alloy prepared with 6.7 wt.%excess Mg was improved compared to the as cast condition.This can be ascribed to a reduction in the thermal conductivity due to phonon scattering at grain boundaries.

Forming-Induced Residual Stress and Material Properties of Roll-Formed High-Strength Steels

Martensitic steels are widely used in the automotive lightweight application but less understood in aspects of post-forming material properties.The steels show good ductility in roll forming but occasionally experience delayed(hydrogen)fracture issues,which are believed to be due to the formation of localized residual stress and a reduced product of strength and elongation.To characterize the effect of roll forming process on the formation of residual stress and material properties variation of martensitic steel components,this paper investigates the forming-induced longitudinal residual stress and material property variation in a roll-formed high-strength MS1180 automotive rocker panel.The finite element analysis results for residual stress are validated by neutron diffraction measurements.The numerical model is used to analyze the full evolution of residual stress during the roll forming process and the effect on material properties with major focus on the product of strength and elongation.It is found that the flower design,in particular the overbending stages,play a significant role in the formation of residual stress and the change in material properties.The product of strength and elongation is significantly reduced across the profile,in particular in the corners.The achieved understanding will assist researchers comprehend the material properties of roll-formed component and therefore assist future studies aimed at preventing the occurrence of hydrogen fracture.