Reducing vehicle weight is an important approach for increasing fuel economy, addressing regulatory requirements, and meeting consumer needs. Magnesium alloys are among the lightest structural metals and offer tremendous weight saving potential; however, many technical and commercial barriers limit their use in today's cars and trucks. Following a brief review of historical trends in vehicle weight and automotive magnesium, we describe key barriers to wider adoption of magnesium in high-volume vehicle applications. A discussion of manufacturing and processing, in-service performance, and cost requirements identifies specific development needs and opportunities while framing promising paths forward.

With nearly twenty years of international research and collaboration in friction stir welding (FSW) and processing industrial applications have spread into nearly every feasible market. Currently applications exist in aerospace, railway, automotive, personal computers, technology, marine, cutlery, construction, as well as several other markets. Implementation of FSW has demonstrated diverse opportunities ranging from enabling new materials to reducing the production costs of current welding technologies by enabling condensed packaging solutions for traditional fabrication and assembly. TMS has sponsored focused instruction and communication in this technology area for more than fifteen years, with leadership from the Shaping and Forming Committee, which organizes a biannual symposium each odd year at the annual meeting. A focused publication produced from each of these symposia now comprises eight volumes detailing the primary research and development activities in this area over the last two decades. The articles assembled herein focus on both recent developments and technology reviews of several key markets from international experts in this area.

As manufacturers strive to improve product performance and reduce weight, particularly in the transportation industries, designers are optimizing material usage with combinations of many different materials and alloys. The goal is to optimize mechanical behavior by selecting material specifically tailored for locations within a product or component. Such mixed material solutions require innovative joining technologies to combine, for example, aluminum and steel or magnesium and carbon fiber composite, etc. Critical to expanding the use of such joined materials in structural applications is the relevant technical understanding of how they form and deform across varying strain rates ranging from superplastic forming to stamping to crash events. With an increasingly rapid development of advanced materials, knowledge gained by assessing the post-weld formability of joined similar and multimaterial structures is crucial to providing the data needed to enable more widespread utilization. On the other end of the spectrum, increased insight characterizing the deformation of these joined structures is also critical to paving the way toward successful implementation. Characterizations via experimentation as well as predictive capabilities are essential to this effort as explored by the articles included in this issue.First, Judy Schneider and Ron Radzilowski provide a history of various processes for joining aluminum and iron-based materials in "Welding of Very Dissimilar Materials (Fe-Al).'' They discuss how welding technologies were developed for specific families of materials followed by the joining of dissimilar materials and how such technologies are implemented in the automotive industry.

Experimental measurements are used to characterize the anisotropy of flow stress in extruded magnesium alloy AZ31 sheet during uniaxial tension tests at temperatures between 350°C and 450°C, and strain rates ranging from 10 -5 to 10 -2 s -1 . The sheet exhibits lower flow stress and higher tensile ductility when loaded with the tensile axis perpendicular to the extrusion direction compared to when it is loaded parallel to the extrusion direction. This anisotropy is found to be grain size, strain rate, and temperature dependent, but is only weakly dependent on texture. A microstructure based model (D. E. Cipoletti, A. F. Bower, P. E. Krajewski, Scr. Mater., 64 (2011) 931–934) is used to explain the origin of the anisotropic behavior. In contrast to room temperature behavior, where anisotropy is principally a consequence of the low resistance to slip on the basal slip system, elevated temperature anisotropy is found to be caused by the grain structure of extruded sheet. The grains are elongated parallel to the extrusion direction, leading to a lower effective grain size perpendicular to the extrusion direction. As a result, grain boundary sliding occurs more readily if the material is loaded perpendicular to the extrusion direction.

A time-dependent material constitutive model is developed for the deformation of wrought Mg AZ31 sheet material at 450°C. This material model is used to simulate gas-pressure bulge forming of AZ31 sheet into hemispherical domes. Finite-element-method (FEM) simulations using this material model are compared against experimental data obtained for dome height as a function of forming time under forming conditions identical to those assumed in the simulations. The time-dependent material model predicts experimental dome heights during forming with a quite useful accuracy. The most significant advantage of the time-dependent material model is that it can address the effect of preheating time on forming. Preheating times shorter than ~120 s produce an increase in forming rate. This material model provides a quantitative means of accounting for that effect.