Grain refinement of Mg-alloys by native MgO particles: An overview

A fine and equiaxed solidification process delivers multidimensional benefits to Mg-alloys, such as improved castability, reduced casting defects, enhanced mechanical properties, increased corrosion resistance and potential for increased recycled contents. Despite extensive research on grain refinement of Mg-alloys in the last few decades, currently, there is no effective grain refiner available for refining Mg-Al alloys, and our current understanding of grain refining mechanisms is not adequate to facilitate the development of effective grain refiners.Under the EPSRC(UK) Li ME Hub’s research program, substantial advances have been made in understanding the early stages of solidification covering prenucleation, heterogeneous nucleation, grain initiation and grain refinement. In this paper, we provide a comprehensive overview of grain refinement of Mg-alloys by native MgO particles. We show that native MgO particles can be made available for effective grain refinement of Mg-alloys by intensive melt shearing regardless of the alloy compositions. More importantly, we demonstrate that(1) the addition of more potent exogenous particles will not be more effective than native MgO;and(2) MgO particles are difficult to be made more impotent for grain refinement through promoting explosive grain initiation. We suggest that the most effective approach to grain refinement of Mg-alloys is to make more native MgO particles available for grain refinement through dispersion, such as by intensive melt shearing.

Novel insight into dry sliding behavior of Cu-Pb-Sn in-situ composite with secondary phase in different morphology

The Cu-24 Pb-x Sn(wt%)(x=0,2,4,6)alloys with Pb-rich second-phase particles(SPPs)in different shapes show obviously differently mechanical and self-lubricating properties.The influence of the SPPs’shape difference on the alloys’mechanical and self-lubricating properties was revealed.Cu-24 Pb alloy with continuously netty SPPs shows much more intensive stick-slip phenomenon during dry sliding than the other three alloys with independently rodlike SPPs.That is mainly due to insufficient lubrication resulted by the netty SPPs’splitting matrix.With the SPPs transforming from netty to rodlike shape under the addition of Sn,the stick-slip phenomenon was notably weakened,which was proven to be related to the higher self-lubricating property of alloys with rodlike SPPs.Simultaneously,the simultaneous increase of ductility and tensile strength was observed in the Cu-24 Pb-x Sn alloys with increasing Sn content,which is because the netty SPPs’splitting behavior will be weakened with them replaced by the rodlike SPPs.