EFFECTS OF HEAT-TREATMENT AND REINFORCEMENT SIZE ON REINFORCEMENT FRACTURE DURING TENSION TESTING OF A SIC(P) DISCONTINUOUSLY REINFORCED ALUMINUM-ALLOY

The effects of heat-treatment, matrix microstructure, and reinforcemen t size on the evolution of damage, in the form of SiC(p) cracking, dur ing uniaxial tension testing of an aluminum-alloy based composite have been determined. A powder metallurgy Al-Zn-Mg-Cu alloy reinforced wit h 15 vol pct of either 5 or 13 mum average size SiC(p) was heat treate d to solution annealed (SA), underaged (UA), and overaged (OA) conditi ons. The SA treatment exhibited lower yield strength and higher ductil ity for both particulate sizes compared to the UA and OA conditions. T he evolution of damage, in the form of SiC(p) fracture, was monitored quantitatively using metallography and changes in modulus on sequentia lly strained specimens. It is shown that the evolution of SiC(p) fract ure is very dependent on particulate size, matrix aging condition, and the details of the matrix-reinforcement interfacial regions. SiC(p) f racture was exhibited by the UA and OA treatment over a range of strai ns, while a preference for failure near the SiC(p)/matrix interfaces a nd in the matrix was exhibited in the OA material. While the percentag e of cracked SiC(p) at each global strain typically was equal or somew hat lower in the material reinforced with 5 mum average size SiC(p), t he absolute number of cracked SiC(p) was always higher at each global stress and strain in the material containing 5 mum average size SiC(p) , for each heat treatment. Damage (e.g., voids) in the matrix and near the SiC(p)/matrix interfaces was additionally observed, although its extent was highly matrix and particle-size dependent. It was always ob served that increases in stress (and strain) produced a larger amount of fractured SiC(p). However, neither a global stress-based nor a glob al strain-based model was sufficient in converging the amount of SiC(p ) fractured for all heat treatments and particle sizes tested.