Avoid cracks on the inner wall of aluminum alloy shell parts

Through the analysis of the macroscopic and microscopic characteristics of the inner surface cracks of the alloy shell parts and the processing process of the parts, the failure causes are finally found and improvement measures are proposed.

By analyzing the chemical composition of the broken part of the faulty part, the content of each element meets the requirements of the relevant standards, so the possibility of cracking on the inner surface of the part caused by the mixing of raw materials is eliminated.

The results of the low-power corrosion test of the failed parts ruled out the possibility of the internal surface cracking of the parts due to serious metallurgical defects.

Aiming at the problem of cracks in the inner wall of the shell parts, the processing process was analyzed in detail. The original processing technology of 2A12 aluminum alloy shell parts is: blanking → car center hole (Ф65) → heat treatment (quenching + natural failure) → car inner hole (Ф140) → failure. The wall thickness of the parts before heat treatment reaches 92.5mm.

The metallographic analysis of the failed parts after heat treatment (quenching + natural failure) shows that the reason for the cracks on the inner wall of the shell parts is that the pipe wall is too thick and the heat treatment is insufficient.

According to the actual situation of aluminum alloy shell parts, the heat treatment process is further optimized, quenching + artificial aging heat treatment. The pit furnace is heated to 495±5℃, kept for 180～210min, and water cooled. No overburning was found in the microstructure, and the aggregation of the strengthening phase along the grain boundary was significantly improved. This proves that the cracks on the inner surface of the part are caused by insufficient heat treatment.

Gear parts processing

Analyzing the processing technology of the faulty parts, it is concluded that when processing to the inadequate heat treatment part, and then maintaining the previous cutting speed and cutting amount, the tool tip part produces stress concentration and acts on the gathering place of the grain boundary strengthening phase, resulting in the crack distribution along the strengthening phase. The direction expanded rapidly.

Through the analysis of the macroscopic and microscopic characteristics of the inner surface cracks of the alloy shell parts and the processing process of the parts, the failure causes are finally found and improvement measures are proposed.

By analyzing the chemical composition of the broken part of the faulty part, the content of each element meets the requirements of the relevant standards, so the possibility of cracking on the inner surface of the part caused by the mixing of raw materials is eliminated.

The results of the low-power corrosion test of the failed parts ruled out the possibility of the internal surface cracking of the parts due to serious metallurgical defects.