INFLUENCE OF FINE-GRAINED STRUCTURE AND SUPERPLASTIC DEFORMATION ON THE STRENGTH OF ALUMINUM-ALLOYS .1. THE PHENOMENOLOGY OF THE INFLUENCE OF FINE-GRAINED STRUCTURE AND SUPERPLASTIC DEFORMATION ON THE STRENGTH OF ALUMINUM-ALLOYS

The influences of fine grained (FG) structure and superplastic deformation on the mechanical properties under quasistatic, impact and cycling loading conditions have been established for the aluminium alloys 1560 (Al-Mg-Mn), 1141 (Al-Cu-Mg-Ni-Fe) and 1960 (Al-Zn-Mg-Cu-Zr). FG materials compared with recrystallized coarse grained (CG) ones improve tensile strength and ductility and high-cycle fatigue endurance, but reduce static and impact toughnesses. The effect of grain refinement on crack resistance is directly manifested in the difficulty of crack initiation and in facilitating its growth. Blanks with FG structure, after superplastic processing, are recommended instead of CG recrystallized ones for the production of principal parts whose service life is limited by first crack appearance. In the presence of cracks, higher strength can be obtained by the use of blanks made of CG commercial semifinished products and those manufactured by traditional methods of hot die forging.