Microstructure Evolution and Growth Orientation of Directionally Solidified Mg–4 wt% Zn Alloy with Different Growth Rates

Abstract

The microstructure evolution and growth orientation of directionally solidified Mg-4 wt% Zn alloy in the growth rate range from 20 to 200 lm/s were investigated. A typical cellular structure was observed with a growth rate of 20 lm/s, and the cellular spacing was 115 lm. When the growth rate increased to 60 lm/s, cellular structure with some developed perturbations was obtained and the cellular spacing was 145 lm, suggesting that the cell-to-dendrite transition happened at the growth rate lower than 60 lm/s. As the growth rate further increased, the microstructure was dendritic and the primary dendritic arm spacing decreased. The relationship between the primary dendritic arm spacings and the growth rates was in good agreement with Trivedi model during dendritic growth. Besides, X-ray diffraction and transmission electron microscopy analyses showed that the growth direction of directionally solidified Mg-4 wt% Zn alloy was 11 20 h ilay in 0002 f gcrystal plane, and the preferred orientation was explained with the lattice vibration model for one-dimensional monatomic chain.

Horizontally Solidified Al–3 wt%Cu–(0.5 wt%Mg) Alloys: Tailoring Thermal Parameters, Microstructure, Microhardness, and Corrosion Behavior

“…Yuan et al [15] processed hypereutectic Nb-Si alloys by directional solidification and have shown that the morphology of the cross section of eutectic cells changed from a square morphology to a nearly round morphology with increasing growth rate. Jia et al [16] used a Bridgman-type DS equipment to investigate the cellular/dendritic microstructural transition, which has been shown to occur for growth rates lower than 60 lm/s. Berkdemir and Gündüz [2] have analyzed Al-5 wt%Cu-(0.5-5) wt%Mg alloys grown in a Bridgman-type furnace at a constant G L equal to 4.84 ± 0.13 K/mm under different G R values varying from 16.7 to 83.3 lm/s.…”

Effect of Ca on Microstructure and Mechanical Properties of Directionally Solidified Mg-Zn-Ca Alloys

“…Moreover, the mechanical and corrosion properties of magnesium alloys may be improved, which is attributed to this columnar structure [8,9]. Recently, the properties of DSed Mg-xZn alloys were studied by Jia et al [10,11], and the results indicate that the mechanical and corrosion properties of alloys with the columnar structure could satisfy the requirements of implant materials. So far, few researches have been conducted on the DSed Mg-Zn-Ca alloys for biodegradable materials.…”