Internal casting defects of die casting (part 2)

6 Non metallic hard point

(1) Features and inspection methods:

In the process of machining or after machining, the appearance inspection or metallographic examination found that there were fine particles or lumps on the casting with hardness higher than that of the metal matrix, which made the tool wear seriously, and often showed different brightness after machining.

(2) Causes:

① Non metallic hard spot; ② mixed with oxide on the surface of alloy liquid; ③ reactant between aluminum alloy and furnace lining; ④ metal material infiltrated with foreign matters; ⑤ inclusion.

(3) Treatment method:

① During casting, do not ladle the oxide on the surface of alloy liquid into the ladle; ② remove the oxide on the surface of iron crucible before coating. Clean the slag on the furnace wall and bottom in time; ③ remove the oxide on the spoon and other tools; ④ use the lining material that does not react with aluminum; ⑤ clean the metal material.

7 Metal hard point

(1) Features and inspection methods:

In the process of machining or after machining, the appearance inspection or metallographic examination found that there were fine particles or lumps on the casting with hardness higher than that of the metal matrix, which made the tool wear seriously, and often showed different brightness after machining.

(2) Causes:

① The hard point of metal is mixed with the element of silicon which is not melted; ② primary silicon: the temperature of aluminum liquid is low, and the storage time is long; ③ Fe and Mn elements are segregated, resulting in intermetallic compounds.

(3) Treatment method:

① When smelting aluminum silicon alloy, do not use silicon element powder; ② when smelting high-speed alloy composition, do not directly add silicon element, and must use intermediate alloy; ③ improve melting temperature and pouring temperature; ④ control alloy composition, especially Fe impurity quality; avoid segregation of Fe, Mn and other elements; ⑤ the content of Si in alloy should not be close to or exceed eutectic composition; ⑥ control the metallography of matrix for raw materials The amount of primary silicon in the structure.

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