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Cast aluminum alloys can be divided into aluminum-silicon alloys, aluminum-copper alloys, aluminum-magnesium alloys and aluminum-zinc alloys according to their chemical composition. Aluminum alloy casting process The casting performance of aluminum alloy is closely related to its chemical composition. Among them, Al-Si alloy is near the eutectic composition and has the best casting performance, similar to gray cast iron. Al-Cu alloy is far away from the eutectic component, has a large solidification temperature range, and has the worst casting performance. In actual production, aluminum castings have riser feeding. The solidification temperature range of Al-Si alloys is small, the riser feeding efficiency is high, and castings with dense structures are easy to obtain. Other types of cast aluminum alloys have a large solidification temperature range, low riser feeding efficiency, and poor casting density. Aluminum alloys are easy to absorb and oxidize, so the pouring system must ensure that the aluminum liquid flows in quickly and smoothly to avoid agitation. Various casting methods are suitable for aluminum alloy castings. When the production volume is small, sand casting can be used, and fine sand should be used for modeling. ； Important castings that are mass-produced use special castings. Metal mold casting has high efficiency and good casting quality. Low pressure casting is suitable for water pressure resistant castings that require high density. Pressure casting can be used for thin-walled and complex small parts. Melting characteristics of cast aluminum alloys: Aluminum alloys are easily oxidized in the liquid state. The product is Al2O3, with a melting point as high as 2050°C and a density slightly greater than that of aluminum. Solid inclusions are suspended in the aluminum liquid and are difficult to remove, which not only worsens the casting performance, but also reduces the mechanical properties and reduces the density of the casting. Liquid aluminum can also easily absorb hydrogen and precipitate during solidification, forming defects such as pores or pinholes. Refining method In order to slow down the oxidation and outgassing of molten aluminum, aluminum alloys should be smelted under a flux layer. KCl, NaCl, etc. can be added to the crucible as a flux to isolate the aluminum liquid from the furnace gas. In order to expel the hydrogen gas that has been sucked into the aluminum liquid and prevent the occurrence of pinholes, hydrogen expulsion refining should be carried out before the aluminum liquid comes out of the furnace. There are many methods. The simpler one is to use a bell jar to press into the aluminum liquid such as zinc chloride (ZnCl2) or hexachloroethane (C2Cl6) and other chlorine salts or chlorides, and the following reaction occurs.: 3ZnCl2 + 2Al = 3Zn + 2AlCl3 3C2Cl6 + 2Al = 3C2Cl4 + 2AlCl3 The boiling point of AlCl3 generated by the reaction is 183°C, and the boiling point of C2Cl4 is 121°C, so bubbles are formed. During the floating process, the gas H2 and Al2O3 inclusions in the aluminum liquid are brought out of the liquid surface together. There are many types of aluminum alloy melting furnaces, and coke crucible boilers are generally used. Resistance crucible boilers can also be used. In addition, induction electric furnaces (power frequency, medium frequency) are also used. The structure of alloys is much more complex than that of pure metals. Because alloys are composed of two or more elements, the interaction between the elements will form various different phases. We call the homogeneous components in metals and alloys that have the same chemical composition, the same structure and are separated from other parts by interfaces as phases. The following analyzes the structures of pure metals and alloys according to this concept. Pure metal is a single phase in liquid state ； The solid state is composed of the same elements and the same crystal lattice, so it is a single phase ； During the crystallization process, there are both liquid and solid phases, which are two phases. When the alloy is in the liquid state, it is a uniform alloy liquid with a certain chemical composition and is a single phase. After the alloy changes from liquid to solid, each element dissolves into each other to form a solid solution ； Elements may also react with each other to form metallic compounds. Solid solution and metal compounds are the two basic phases of solid alloys. Therefore, when the alloy is in the solid state, it may be a single-phase structure or a multi-phase structure. When analyzing the alloy structure, it is to analyze its phase structure to see how many solid solutions or metal compounds it consists of, that is, how many phases it consists of. This post was last edited by yutr on 2009-3-29 13:14 ]