Prevention of Zinc Sublimation from Alclad Vacuum Brazing Sheet by Calcium Addition to 7072 Cladding

7072 alclad sheet has long been applied for aluminum heat exchanger components because of the excellent cathodic protection.

However, the sacrificial anode effect of 7072 cladding would be impaired by zinc sublimation during vacuum brazing cycles.

This paper describes the effect of additional calcium to 7072 cladding on zinc sublimation in vacuum brazed alclad sheet.

For lighter gauge (0.4 mm), 7072 cladding does not provide adequate retained zinc after vacuum brazing, but 7072 cladding with calcium will have sufficient retained zinc to afford galvanic protection to the core.