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Magnesium alloys are of growing research, development and commercial interest for their lightweight characteristics, notably in the automotive sector. Recent results based on experiments and simulations of beam components have shown that finite element (FE) predictions using commercial FE software may significantly overestimate the peak load and load beyond the peak load. This indicates that better deformation and failure criteria are needed for crashworthiness simulation and design of Mg alloys for the development of computer-assisted engineering (CAE) capacity for Mg alloys. In this study, yield and hardening laws for deformation simulation of Mg alloys are reviewed. An isotropic Lode angle dependent von Mises yield and flow model originally used for soil was modified by replacing shear strength with tensile or compressive flow strength for deformation simulation of Mg alloys.

Facing the challenge of lightweighting and energy consumption efficiency, aluminum extrusions (e.g. AA6060-T6 and AA6082-T6) may be used to replace steel for bumpers and other crash management systems (CMS). Robotic gas metal arc welding (GMAW) is currently used to weld the beam and bumper box. In order to better understand the crashworthiness of the beam, there is significant interest to obtain constitutive behavior of heat affected zone (HAZ) and weld metal. A new test procedure has been developed to couple both tensile test and shear test with the digital image correlation method to directly measure constitutive behavior of different regions in GMAW welds, namely base metal, HAZ and weld metal. The test procedure has been applied to welds of AA6060-T6 and AA6082-T6 extrusions made using conventional robotic GMAW.

Effects of strain rate and temperature on tensile, compressive and toughness properties were investigated for an extruded Mg alloy AM30 in both extrusion (ED) and transverse (TD) directions. The effects of strain rate and temperature on uniaxial flow stress were reported elsewhere but will be briefly described to facilitate the understanding of Charpy results (i.e., load, deflection and absorbed energy). The effects of loading rate from quasi-static to 5.1 m/s on un-notched and V-notched Charpy load-deflection curves up to maximum load were negligible, but load up to maximum load increased with decreasing temperature. The deflection at rapid load-drop in un-notched Charpy tests increased with decreasing loading rate and increasing temperature between -50°C and 100°C for un-notched ED and TD specimens (i.e., L-T and T-L specimens according to ASTM E 1823 terminology).

Engineering stress analysis of bolt joints requires knowledge of the stiffness of the joints. One convenient way to estimate stiffness of joints is to use effective stress area equations because only part of the joint surface carries load. In this work, the existing effective stress area equations (developed about 50 years ago) were assessed using a washer/joint contact finite-element (FE) model. It was found that these equations may underestimate the effective area and the joint stiffness by as much as 50%. Typical bolt-load retention (BLR) test fixtures were modeled using a commercial FE code. In the simulation, the creep stress-strain behaviour of a magnesium alloy was described by a three-parameter power-law relation that was fitted from the compressive creep test results of a high-pressure die-casting (HPDC) Mg alloy (AM50). The bolt-load vs. time relationships from FE simulation were compared with those obtained experimentally, and they showed good agreement.

For automotive applications at elevated temperatures, the need for sufficient creep resistance of Mg alloys is often associated with retaining appropriate percentages of initial clamp loads in bolt joints. This engineering property is often referred to as bolt-load retention (BLR); BLR testing is a practical method to quantify the bolt load with time for engineering purposes. Therefore, standard BLR test procedures for automotive applications are desired. This report summarizes the effort in the Structural Cast Magnesium Development (SCMD) project under the United States Automotive Materials Partnership (USAMP), to provide a technical basis for recommending a general-purpose and a design-purpose BLR test procedures for BLR testing of Mg alloys for automotive applications. The summary includes results of factors influencing BLR and related test techniques from open literature, automotive industry and research carried out in this laboratory project.

This study details preliminary results of hot rolling trials of AZ31 alloy sheet using a pilot-scale rolling mill. The aim is to design and optimize the hot rolling schedule for AZ31 in order to produce sheet with a fine and homogeneous microstructure. The study examined three different hot rolling temperatures, 350, 400 and 450°C and two rolling speeds, 20 and 50 RPM. A total thickness reduction of 67% was obtained using multiple passes with reductions of either 15% or 30% per pass. The entry temperature of each rolling schedule was kept constant, by reheating the strip between passes. It was found that the microstructure of the AZ31 alloy was sensitive to the rolling temperature, the reduction (i.e. strain) per pass and the rolling speed (i.e. strain rate). A combination of a rolling temperature of 400°C, reduction per pass of 15%, and rolling speed of 50 RPM produced the finest and most homogeneous microstructure.