Research On The Water-soluble Salt Core Used For High-pressure Casting

The water-solube salt cores have good collapsibility, so they are easy to clear up. But in the squeeze casting process with complex shapes cavity in the casting, the exiting salt cores would be broken. The aim of this paper was to develope a sort of high strength salt core used for aluminum alloy squeeze casting. This paper had researched the bending strength of binary systems NaCl-Na₂SO₄, NaCl-Na₂CO₃ and Na₂CO₃-Na₂SO₄, and NaCl or Na₂SO₄ composite salt cores enforced by ceramic reinforcements, and also the forming characteristics of salt cores. The main conclusions are summarized as followings:(1) The binary system salt cores had lower surface roughness concentration than unary salt cores. The systems NaCl-Na₂SO₄ and NaCl-Na₂CO₃ had formed shrinkage cavity, but system Na₂CO₃-Na₂SO₄ salt cores had no shrinkage cavity.(2) The bending strength of systems NaCl-Na₂SO₄ and NaCl-Na₂CO₃ were higher than unary salt cores, which were the highest one at the composition between eutectic and the unary. When the proportion of Na₂SO₄ was 30mol%, the system NaCl-Na₂SO₄ had the highest bending strength of 20.9MPa; but when the proportion of Na₂SO₄ was between 40-90mol%, salt cores cracked, even fractured. When the proportion of Na₂CO₃ was 30mol%, the NaCl- Na₂CO₃ salt core had the highest bending strength of 21.5MPa. The system Na₂CO₃-Na₂SO₄ had lower strengh, when the proportion of Na₂SO₄ was 70mol%, salt cores had the highest bending strength of 5.8MPa.(3) The Al2O3 particles (48-75μm) had enforced the NaCl and Na₂SO₄ composite salt cores.There were surface folds on all composite salt cores, and Na₂SO₄ composite salt cores had more surface folds than NaCl composite salt core. Ceramic reinforcements could refine equiaxed zone grains of salt cores. When the addition of ceramic reinforcement exceeded the maximum, the composite salt cores would produce large shrinkage cavity. As the content of Al2O3 particles increased, the shrinkage rate of NaCl salt cores declined, and shrinkage rate of Na₂SO₄ salt cores declined firstly and then ascended. The content of Al2O3 particles had increased the water-soluble time of composite salt cores.(4) The bending strength of composite salt cores increased with the content of reinforcement increasment. The NaCl composite salt cores had been enforced by Al2O3 particles,SiO₂ particles and Aluminium borate whisker separately, when the content of Al2O3 particles (48-75μm) was 33.3wt%, the NaCl composite salt core had the highest bending strength, up to 20.2MPa. The Na₂SO₄ composite salt cores had been enforced by Al2O3 particles,SiO₂ particles,MgO particles and Aluminium borate whisker separately, when the content of SiO₂ particles was 21.7wt%, the Na₂SO₄ composite salt core had the highest bending strength, up to 16.2MPa.(5) A set of squeeze casting mold was designed for fabrication of complex water-soluble salt core. The complex NaCl composite salt cores were prepared by squeeze casting which enforced by 28.5wt% Al2O3 particles (48-75μm). The bending strength of complex salt core was 21.29MPa.