An Investigation of the Structure and Properties of Aged Aluminium Bronzes

Abstract

The ageing response of wrought single phase aluminium bronze alloys containing additions of cobalt up to 1% is assessed for use as a bolting material by mechanical tests, microstructural examination, and constant strain rate stress corrosion trials. The dependence of mechanical properties on cobalt concentration, degree of ageing and level of cold work is established. The presence of a precipitation hardening mechanism is identified. The hardening phase in the final stages of the precipitation sequence is shown to be a compound based on CoAl having an orientation with respect to the matrix of [101] m|| [lil] ppt, (111) m || (110) ppt. A susceptibility to stress corrosion cracking is established for the alloy system. Two basic mechanisms are identified 1) A strain-generated active path mechanism for solutions of pH=12 and 2) a pre-existing active path mechanism for a sea water environment. The susceptibility to stress corrosion cracking in seawater is shown to depend on the metallurgical condition of the alloy.