Microstructure analysis of freeze-cast A356 aluminum alloy

In combination with the digital and green development needs of the foundry industry, this article proposes a digital patternless freezing casting method. In this method, mixed water green sand particles are frozen and transformed to a certain strength in a low-temperature environment, which are then directly cut through a sand mold CAD three-dimensional model. Pouring to obtain castings with dimensional accuracy that meets the requirements, this is a new technology, new process, and new method in the field of casting. With the fast development of the rapid and sub-rapid solidification technology of metals, the nonequilibrium solidification theory of liquid–solid transformation during the preparation of metals and alloy materials has been developed by leaps and bounds. Using some special nonequilibrium solidification techniques to prepare metal parts, and to make metal parts with a special structure that traditional casting does not have, can improve the materials’ properties and structures. The nonequilibrium solidification mechanism based on the freezing casting technology is not yet clear. Based on the nonequilibrium solidification process of the freezing casting principle, a higher cooling rate will considerably affect the heat transfer and mass transfer behavior of casting during solidification, which will then considerably affect the alloy micro component distribution and fracture morphology, ultimately affecting the service performance of the alloy material. Based on the digital precision forming technology of patternless frozen casting, this paper realized the rapid forming of the frozen sand mold. Frozen casting flat castings were obtained by pouring the A356 high-temperature aluminum alloy. The distribution of trace elements in frozen and resin sand castings was characterized by electron probe microanalysis, and the fracture morphology of frozen and resin sand castings was analyzed. Results show that the solubility of the Si element in the aluminum matrix phase of freeze casting is significantly higher than that of resin sand casting. In addition, the distribution of the Mg element in freeze casting is more uniform than that in resin sand casting, and there are more segregation areas of the Mg element composition in resin sand casting specimens. The fracture morphology of freeze-cast specimens is a mixed fracture mode of toughness and brittleness. Meanwhile, the fracture morphology of resin sand casting specimens has a cleavage step failure morphology and rectangular tear structure morphology, and the alloy tends to exhibit a brittle fracture.