The mold temperature of the downward continuous unidirectional solidification (CUS) cannot be controlled higher than the liquidus of alloys to be cast. Therefore, the continuous casting speed becomes the main parameter for controlling the growth of columnar crystal structure of the alloy. In this paper, the tin bronze alloy was prepared by the downward CUS process. The microstructure evolution of the CUS tin bronze alloy at different continuous casting speeds was analysed. In order to further explain the columnar crystal evolution, a relation between the growth rate of columnar crystal and the continuous casting speed during the CUS process was built. The results show that the CUS tin bronze alloy mainly consists of columnar crystals and equiaxed crystals when the casting speed is low. As the continuous casting speed increases, the equiaxed crystals begin to disappear. The diameter of the columnar crystal increases with the continuous casting speed increasing and the number of columnar crystal decreases. The growth rate of columnar crystal increases with increasing of the continuous casting speed during CUS tin bronze alloy process.

The exudation layer seriously affects the properties and the surface finish of the tin bronze alloy. The effective control of the exudation thickness is important measure for improving the properties of the alloy. In order to study the influence of process parameters on the thickness of exudate layer, the tin bronze alloy was prepared by continuous unidirectional solidification technology at different process parameters. The microstructure of the continuous unidirectional solidification tin bronze alloy was analyzed. The effect of process parameters on microstructure and chemical compositions was studied by orthogonal experiment. The results show that there exists an exudation layer on the surface of the continuous unidirectional solidification tin bronze alloy, and the exudation is mainly composed of a tin-rich precipitated phase. It indicates that the continuous casting speed is the main factor affecting the thickness of exudation layer, followed by mold temperature, melt temperature, cooling water temperature and cooling distance.

Investigation of the tensile and fatigue properties of cast magnesium alloys, created by the heated mold continuous casting process (HMC),

was conducted. The mechanical properties of the Mg-HMC alloys were overall higher than those for the Mg alloys, made by the

conventional gravity casting process (GC), and especially excellent mechanical properties were obtained for the Mg97Y2Zn1

-HMC alloy.

This was because of the fine-grained structure composed of the -Mg phases with the interdendritic LPSO phase. Such mechanical

properties were similar levels to those for conventional cast aluminum alloy (Al84.7Si10.5Cu2.5Fe1.3Zn1 alloys: ADC12), made by the GC

process. Moreover, the tensile properties (UTS and f

) and fatigue properties of the Mg97Y2Zn1

-HMC alloy were about 1.5 times higher

than that for the commercial Mg90Al9Zn1

-GC alloy (AZ91). The high correlation rate between tensile properties and fatigue strength

(endurance limit: l

) was obtained. With newly proposed etching technique, the residual stress in the Mg97Y2Zn1 alloy could be revealed,

and it appeared that the high internal stress was severely accumulated in and around the long-period stacking-order phases (LPSO). This

was made during the solidification process due to the different shrinkage rate between α-Mg and LPSO. In this etching technique, microcracks

were observed on the sample surface, and amount of micro-cracks (density) could be a parameter to determine the severity of the

internal stress, i.e., a large amount to micro-cracks is caused by the high internal stress.