Microstructure and mechanical properties of mechanically alloyed, ingot metallurgy and powder metallurgy AlLiCuMg alloys

Abstract

AlLiCuMg alloys with similar chemical compositions were prepared by mechanical alloying, ingot metallurgy and powder metallurgy. Their microstructures and their monotonic and fatigue properties were investigated. All three types of alloy exhibited low ductility, a problem typical of the high modulus, low density AlLi-base alloys. In the assolution-treated condition, uniformly distributed fine particles of oxide and carbides gave a reasonable strength to the alloy prepared by mechanical alloying. Although these particles homogenized the deformation, the presence of larger second-phase particles caused premature crack initiation and low tensile ductility. When alloys prepared by ingot metallurgy and powder metallurgy were deformed in the underaged and slightly overaged conditions, the shearable coherent Al 3Li (δ′) particles that were present promoted planar slip, strain localization and low ductility. A low cycle fatigue study showed that no break was observed in the Coffin-Manson plot, suggesting that no change in the deformation mode occurred in the high and low strain amplitude tests. Also, because of the more homogeneous deformation the alloy prepared by mechanical alloying exhibited a higher fatigue resistance than the alloys prepared either by ingot metallurgy or by powder metallurgy of similar tensile strength.