Intergranular corrosion susceptibility for Al–Mn–Cu alloys subjected to heat treatment at 180°C after brazing process

• Published in: Journal of Japan Institute of Light Metals Vol. 62; no. 5; pp. 206 - 211
• Main Authors: Oya, Yoshiyuki, Tanaka, Satoshi, Ninomiya, Junji, Doko, Takeyoshi, Kojima, Yoichi
• Format: Journal Article
• Language: Japanese
• Published: Tokyo The Japan Institute of Light Metals 30.05.2012; Keikinzoku Gakkai, c/o Hibiya Asahi Seimeikan, Keikinzoku Kyokai
• Subjects: acetic acid; aluminum alloy; corrosion test; pitting corrosion
• ISSN: 0451-5994; 1880-8018
• DOI: 10.2464/jilm.62.206

The alternation of an air-conditioner refrigerant from a freon-based refrigerant to CO2 is proposed. A maximum temperature in the CO2 heat-exchange cycle approaches to 180°C after brazing, which might affect susceptibility to intergranular corrosion. In this work, the intergranular corrosion susceptibility of Al–Mn–Cu alloys heat treated at 180°C after brazing was investigated. In both of the heat treated and non-treated Al–Mn–Cu alloys, Al–Cu intermetallic compounds were observed at grain boundaries, while in the non-treated Al–Mn–Cu alloys, Al–Mn intermetallic compounds also existed at the grain boundaries, being in contact with the Al–Cu compounds. The observation indicates that the Al–Mn compounds promote precipitation of the Al–Cu compounds at the grain boundaries. It also means development of Cu depleted zone along the grain boundaries. However, the intergranular corrosion susceptibility was decreased when the heat-treatment time become longer because Cu solid solubility in the grains decreased down to the same level of the Cu depleted zone. With the Mn concentration, the decreasing rate is accelerated and the time needed to show no susceptibility is shortened.