Grain refinement via semi-solid deformation is desired to obtain superior mechanical properties of cast components. Using quantitative in situ synchrotron X-ray tomographic microscopy, we show an additional mechanism for the reduction of grain size, via liquation assisted transgranular cracking of semi-solid globular microstructures. Here we perform localized indentation of Al-15wt.%Cu globular microstructures, with an average grain size of ∼480 μm, at 555 °C (74% solid fraction). Although transgranular fracture has been observed in brittle materials, our results show transgranular fracture can also occur in metallic alloys in semi-solid state. This transgranular liquation cracking (TLC) occurs at very low contact stresses (between 1.1 and 38 MPa). With increasing strain, TLC continues to refine the size of the microstructure until the grain distribution reaches log-normal packing. The results demonstrate that this refinement, previously attributed to fragmentation of secondary arms by melt-shearing, is also controlled by an additional TLC mechanism.

中文翻译：

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半固态晶粒的经晶化液化开裂。

需要通过半固态变形来细化晶粒以获得铸造部件的优异机械性能。使用定量原位同步加速器X射线断层扫描显微镜，我们显示了通过液化辅助半固态球状显微组织的穿晶裂纹减少晶粒尺寸的另一种机制。在这里，我们在555°C（固含量为74％）下对Al-15wt。％Cu球状微结构进行局部压痕，平均晶粒尺寸约为480μm。尽管已在脆性材料中观察到了经晶断裂，但我们的结果表明，经晶断裂也可在半固态金属合金中发生。这种跨颗粒液化开裂（TLC）在非常低的接触应力（1.1至38 MPa之间）下发生。随着压力的增加，TLC继续细化微结构的尺寸，直到晶粒分布达到对数正态堆积。结果表明，这种精细化以前还归因于通过熔体剪切而导致的次级臂断裂，还受到其他TLC机制的控制。