Effects of Si Content and Forging Pressure on the Microstructural and Mechanical Characteristics in Semi-solid Forging o
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RODUCTION
RECENT research on automobiles with respect to materials has focused on reducing the weight of components. The focus on improving fuel and energy efficiency has driven the development of aluminum alloys with high mechanical properties as an alternative to steel alloys.[1–4] In the automotive industry, diecasting and hot forging are the main methods for manufacturing aluminum products. The diecasting process is advantageous for mass production, but there is difficulty in obtaining high mechanical performance due to pore and shrinkage defects. The hot forging process is able to
BYUNG KEUN KANG and IL SOHN are with the Department of Materials Science and Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul, 03722, Republic of Korea. Contact e-mail: [email protected] Manuscript submitted November 22, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS A
achieve better mechanical properties, but the productivity is low owing to additional heat processing of the billets and molds.[5] As an alternative manufacturing method for processing aluminum alloys, which can be beneficial for both productivity and mechanical properties, semi-solid metal-forming processing has been developed.[6–10] SSF processing is known to improve the quality and mechanical properties of products with low pore and shrinkage defects. A rheo-forming process, which is one type of semi-solid metal-forming process, utilizes a strong stirring action in the liquid metal, enhancing the formation of a semi-solid slurry.[11] Various studies regarding the improvement of semi-solid processing have been conducted, including stirring methods for making slurries, such as mechanical stirring, electromagnetic stirring, and ultrasonic treatments. Slurry-making process parameters, such as pouring temperature and solid fraction, and manufacturing methods of the semi-solid slurry for casting and forging have also been studied.[10,12–18]
In the case of rheo-diecasting, a semi-solid forming process, the product size and thickness are limited due to shrinkage defects.[8] On the other hand, the semi-solid forging process has greater flexibility to manufacture products with varying thicknesses and sizes and enhanced mechanical properties due to the higher pressure in comparison to that of the rheo-diecasting method. In the semi-solid forging process, a lower forging pressure is required compared to that required in the typical forging process due to the coexistence of solid and liquid phases within the melt. Thus, semi-solid forging can be useful in the production of aluminum alloys with better mechanical performance and lower production cost than those produced by other manufacturing processes, such as forging or diecasting.[19] Semi-solid forging of conventional commercial aluminum alloys has been studied to improve the quality of the product[10,20,21] and the mechanical properties of the resultant alloys.[22–25] For the improvement of the quality of semi-solid product, grain refinements,[10] process parameters, and cooling system[21] have been studied. H
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