Through the quantitative characterization of eutectic structure under different pressures, it can be seen that the morphology of each phase in the structure has changed significantly, as shown in the figure. The most obvious change is the refinement of eutectic structure, and the characteristic quantity of this phenomenon is eutectic spacing. The eutectic spacing usually refers to the average spacing, which is measured by Image Pro Plus 6.0.

It can be seen that the eutectic spacing of hypoeutectic alloy 1 # or hypoeutectic alloy 2 # decreases with the increase of pressure. However, the influence law is slightly different. In hypoeutectic alloy 1 # the decrease of eutectic spacing is not very obvious, and the error is very large, which indicates that the distribution of eutectic phase is very uneven, as shown in figure (a). When the pressure increases to 100 MPa, the eutectic spacing decreases by about 30%, but when the pressure continues to increase to 170 MPa, the eutectic spacing is almost the same as that of 100 MPa.

The eutectic spacing of near eutectic alloy 2 # decreases significantly with the increase of pressure, as shown in figure (b). When the pressure increases from atmospheric pressure to 160 MPa, the eutectic spacing decreases by about 10% μ m. About 50% reduction. The deviation of eutectic spacing decreases with the decrease of pressure, which indicates that the phase distribution in eutectic structure is more uniform with the increase of pressure.