Studies on the Digital Expression of Al-Si Alloy Microstructure and Its Applications in Properties Analysis

In traditional metallograph analysis, the results were often varied from different observers. The concept of digital expression of Al-Si alloy microstructure was put forward, and the procedures of digital expression were also discussed in detail. This method was fit for processing the microstructure with granular secondary phase especially, and the results were certainly and could be reported in digital style with good comparability. A permanent mould Al-12wt%Si alloy casting with different wall thickness was designed to illustrate the application of microstructure digital expression. Some unusually results were found such as self-tempering and relation between microstructure and hardness in the digital processing of microstructure. The experimental results also showed that the primary silicon precipitated as needle like shape in thick and thin section, but as granule like shape in the transitional section. The finer and shorter of the needle like β-phase, the higher hardness of the sample possessed. And in general, the hardness in transitional section with granule β-phase was lower than those sections with needle β-phase. It was also found that the total average mean diameter were 1.326, 1.250 and 1.263 um respectively from thick section to thin section of the casting.