Homogenization heat treatment influence on microstructure evolution and mechanical properties of as-cast Al–Li–Cu–Mg–Zr alloy for lightweight aerospace application

Abstract

Al–Li–Cu–Mg–Zr alloys are widely used in the aerospace industry for different applications and make an excellent concurrent to high-performance composites. This family of alloys has remarkable properties like low density, high elastic modulus, high strength and specific stiffness, fracture toughness, fatigue crack growth resistance, and improved corrosion resistance.The present work aims to investigate a family of Al–Li alloys by employing suitable characterization techniques such as computer-aided cooling curve analysis and thermal dilatometry to characterize the as-cast alloy. The characterization temperatures of the alloy were obtained and the phase transformation temperatures were concluded as thermal expansion inflection points as well. Furthermore, the homogenization heat treatment effect of the alloy is examined through optical microscopy (OM), scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and Vickers microhardness testing to determine the optimum heat treatment time. The results reveal the formation of δ′, δ and β’ precipitates in the alloy after different hours of homogenization heat treatment. Notably, our investigation identifies the optimum heat treatment time for the alloy as 26h at 515 °C, resulting in reduced hardness and barely any chemical segregation. These findings contribute to the characterization of as-cast Al–Li alloys and the understanding of microstructure evolution and mechanical properties during homogenization heat treatment that offer a valuable insight for enhancing their performance in aerospace applications.

Keywords

• Al-Li-Cu-Mg-Zr alloy
• Homogenization heat treatment
• Mechanical properties
• Microstructures
• Precipitates
• Microsegregation