Nucleation and propagation of tensile twins in magnesium alloy AZ31 are investigated for a large number of twins at an early stage of their development. High-resolution electron backscatter diffraction (HREBSD) techniques are employed to give additional insights. Correlations with grain orientation, boundary misorientation and active slip systems are observed in the region of twins that arise at grain boundaries. Two types of twin are identified: 1) slipassisted twins that nucleate at grain boundaries with no apparent influence from nearby twins, and 2) twin-assisted twins that result from twins propagating across a grain boundary. Twinning occurs in "hard" grains that cannot accommodate necessary contraction via -type slip. Slip assisted twins nucleate at high-angle boundaries. Twin-assisted twinning occurs at low-angle boundaries. The distributions of grain boundary misorientation associated with each type of twin

Friction stir welding was investigated as a viable process for joining thin aluminum sheets in order to manufacture tailored blanks. In the present study three alloys were tested: 5182-O, 5754-O, and 6022-T4. All three of these alloys are being used to fabricate stamped automotive parts. The gas tungsten arc welding process has been used to make aluminum-tailored welded blanks industrially, so results using this process were compared to FSW results. Blanks of the same gage of all three alloys were welded and then evaluated using tensile and formability testing. The 5xxx series alloys had similar tensile ductility and formability regardless of the welding process. However, the 6022-T4 sheets joined using friction stir welding had better formability than those joined using gas tungsten arc welding because friction stir welding caused less softening in the heat-affected zone.

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A new spot joining technology relying on a consumable joining bit has been developed and evaluated on dual phase (DP) 980 steel and a dissimilar combination of aluminium alloy 5754-O and DP 980. This new process, called friction bit joining (FBJ), uses a consumable bit to create a solid state joint in sheet materials by the action of cutting and frictional bonding. FBJ lap shear fracture loads were 14?7 kN for 1?4 mm DP 980 compared to 16?6 kN for RSW, for the same spot diameters. FBJ of a dissimilar combination of aluminium alloy 5754-O and DP 980 produced joints with average lap shear fracture load of 6?3 kN. This strength is greater than lap shear fracture load obtained by self-piercing riveting (SPR) in HSLA 350 bonded to AA 5754-O.

The use of high strength steels (HSS) and ultra high strength steels (UHSS) is increasing in automotive applications to reduce vehicle weight and to improve structural performance. This study focused on the properties and microstructures of friction stir welded steel sheets, as a function of welding conditions. Tooling feeds and speeds had a significant impact on mechanical properties and microstructures of the welds. For example, at constant tool speeds higher feedrates produced softer welds with large amounts of primary ferrite, compared with lower feedrates which produced harder welds and a greater fraction of martensite. These results illustrate the potential of adjusting weld properties and microstructures by using different friction stir welding process conditions for HSS and UHSS alloys.