DEVELOPMENT OF A HIGH-STRENGTH STRESS-CORROSION-RESISTANT ALLOY WITH AN ALZNMG BASE. PART II. INFLUENCE OF CHEMICAL COMPOSITION ON ARTIFICIAL AGE HARDENING AND STRESS CORROSION OF HIGH-STRENGTH ALZNMGCU ALLOYS

The experimental results described in Part I of this report Aluminium Vol 39 1963. No 5. pp 290-297. and No 10, pp 630-637 demonstrated that it would be necessary to overcome the stress corrosion in high strength alloys of the AlZnMgCu type also in the critical vertical direction of large extruded bars. It was found that the chromo effect in the aforementioned direction, which is generally considered to be very favorable, may be superposed or even made ineffective by the presence of lines of undissolved intermetallic phases. The question as to whether in this connection the aluminide of iron, chronium and manganese. or a copper.containing phase were particularly harmful could not yet be answered. rthy of note was the very good behavior of alloys of the W-3435 type. in which the usual ccpper additive was wholly or partially replaced by silver. By using age-hardening temperatures of above 140 C, the stress corrosion would be eliminated in this kind of alloys also in the vertical direction.