Fabrication of high-strength salt cores for manufacturing hollow aluminum alloy die castings

In this work, the high-strength composite salt cores reinforced by corundum powder were successfully prepared using 30 mol% Na2SO4 +70 mol% NaCl as the matrix materials, which can be used to fabricate hollow aluminum alloy die castings with complex structures. The influences of the content and size of corundum powder on properties and microstructures of Na2SO4-NaCl composite salt cores were investigated, and the strengthening mechanisms of the salt cores were analyzed. The results show that the flexure strength of Na2SO4-NaCl composite salt cores increases first and then decreases with the increase of the corundum powder content, and appropriately reducing the corundum powder size is beneficial to improving the flexure strength. The maximum flexure strength of Na2SO4-NaCl composite salt cores reinforced by corundum powder with multi-size hybrid can reach 59.08 MPa, increasing by 219.3% compared with the unreinforced salt cores, and the linear shrinkage rate and water-solubility rate are 1.56% and 231.9 g/(min center dot m(2)), respectively. The microscopic analysis shows that the corundum powder can remarkably refine the NaCl primary phase, which completely changes from coarse dendrites to fine equiaxed crystals, improving the flexure strength. Meanwhile, the flexure strength enhancement is also attributed to prolonging the crack propagation path.