A356 is a cast aluminum alloy, non-die cast aluminum alloy. It is mainly used for structural parts with high strength and good elongation. Fe element exists as impurity, and the content of Fe affects the elongation of aluminum castings. The higher the content of Fe, the more brittle the aluminum castings are.
As you may know, the Fe content of A356 is less than 0.2%, and the Fe content of A356 aluminum ingot is less than 0.12%. However, the die-casting process requires a certain Fe content, at least 0.5% or more, so as to facilitate demoulding. Therefore, the Fe content of aluminum alloy generally used in the die-casting process is relatively high, and the Fe content of many die cast aluminum alloys is 0.5-1%, while the low Fe content of A356 will lead to serious sticking and demoulding during die casting process. Therefore, from this aspect, the die casting process is not suitable for producing A356 aluminum castings.
On the other hand, to achieve good strength, T6 heat treatment needs to be performed after casting of A356 aluminum alloy. During the T6 heat treatment process, A356 aluminum castings should keep warm in the 535℃ or so in the furnace for about 8 hours. However, the melting point of A356 aluminum alloy is 555-615℃, that is to say, aluminum alloy will start to melt when the temperature reaches 555℃. So at the high temperature of 535℃, aluminum castings have been close to melting. At this time, if there is gas in aluminum castings, the gas will be precipitated to the surface of the casting from the inside, forming a large number of small bumps on the surface of castings, which leads to the rejection of castings. While the characteristics of die casting process is to shoot the aluminum water through the plunger at high speed into the mold cavity, and will entrap a lot of gas into the mold cavity. Although the exhaust is set up in the mold, the gas enwrapped in the aluminum water can not be discharged, and will eventually stay in aluminum castings. Therefore, after 535℃ of heat treatment, the surface will form a large number of bumps, the strength of the product can not reach, the appearance can not be used.