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Current commercial magnesium extrusion alloys do not offer desirable combinations of strength, ductility, and extrusion speed for automotive structural applications. The effect of small additions of cerium (Ce) to pure magnesium (Mg) and Mg-3 pct Al alloy extruded tubes has been studied. The results suggest that 0.2 pct Ce addition can significantly improve the extrudability and mechanical properties of the Mg extrusions. The improvement in mechanical properties is due to grain refinement and dispersion strengthening provided by the MgCe particles and the beneficial texture obtained. Higher Ce contents further increase strength, but significantly reduce ductility and cause excessive surface oxidation during extrusion. The beneficial effect of 0.2 pct Ce on mechanical properties of pure Mg is not observed when it is added to Mg-3 pct Al alloy, due to the higher affinity of Ce to Al to form the AlCe phase in the Mg-Al-Ce ternary alloys. The Mg-0.2 pct Ce alloy is a promising base alloy for further development in automotive applications; however, Al should be avoided in Mg-Ce–based extrusion alloys. [ABSTRACT FROM AUTHOR]

The Co-based alloy 2.4711 investigated in this study consists of an austenitic martix with ε-martensite from both strain hardening and aging. Upon deformation, the microstructure shows strain-induced γ→ε transformation. Mechanical twinning could not be verified in this study using EBSD. Tensile testing in hydrogen gas and with H-precharged specimens revealed negligible embrittlement for the specimens tested in H 2 gas, whereas severe embrittlement was found for the H-precharged specimen. This was interpreted and explained by hydrogen transport during the two test configurations. It appears that the ε-martensite in alloy 2.4711, unlike strain-induced martensite in type 304 austenitic stainless steels, does not enhance hydrogen ingress over long distances during tensile testing in gaseous hydrogen. Limiting hydrogen transport during testing in gaseous hydrogen precludes observation of intrinsic hydrogen effects, while saturation of hydrogen by H-precharging illuminates intrinsic hydrogen sensitivity. [ABSTRACT FROM AUTHOR]