Abstract: The effects of Zr on the microstructures and mechanical properties of microalloyed steels have been investigated by mechanical tests and microstructural observations. The microstructures in the Zr-doped steels are ferrite plus pearlite, which is similar to those in the Zr-free steel. With the increase in the Zr content, the lamellar structure reduces and even disappears. Sulfides and silicates that exist in the Zr-free steel are modified into fine oxides in the Zr-bearing steel. When the Zr contents range from 0.01wt% to 0.03wt%, the low temperature toughness of the steel can be substantially improved while its room-temperature strength and ductility have no apparent change. The refinement of ferrite grain size by the addition of zirconium is one of the main reasons for this toughness improvement. KEY WORDS zirconium; microalloyed steel; microstructure; mechanical property 20060010 A novel semi-solid slurry-making process was developed, which was a controlled nucleation and growth technique using a specially designed rotational barrel. Experimental study was undertaken to investigate the effects of pouring temperature and rotation speed of barrel on the microstructure of A356 alloy. Localized rapid cooling, combined with vigorous mixing during the initial stage of solidification enhanced wall nucleation and nuclei survival. High nuclei density combined with a much gradual cooling afterwards led to the formation of the near-ideal semi-solid slurry under a large processing window for the pouring temperature. Primary phase presented in mean equivalent diameter of 50-70μm and shape factor of 0.812-0.847, and featured zero-entrapped eutectic. KEY WORDS semi-solid processing; nucleation; grains growth; interface stability 20060011 Macro-texture of an Mg-Al-Ca alloy prepared by friction stir welding (FSW) was investigated through pole figure measurement and X-ray diffraction (XRD) pattern analysis. It was found that at the top and bottom surfaces of friction stir zone (FSZ), (0002) basal planes of magnesium tend to be arranged parallel to the plate surface. In the cross section of FSZ, no obvious texture had evolved and (0002) basal planes showed a random distribution.

Key words: zirconium, microalloyed steel, microstructure,