Extraction and X-ray analysis of phases in aluminium alloys

Abstract

The extraction of precipitates and second phase insoluble intermetallic or metalloid compounds from three commerical aluminium alloys was achieved by anodic dissolution of the aluminium alloy matrix in a methanolic electrolyte containing benzoic acid, oxine and chloroform. Investigated were Aluminium Association alloy 7075 containing principally Al-Zn-Mg-Cu, alloy 6061 containing principally Al-Si, and alloy 2011 containing principally Al-Cu. X-ray diffraction of the extracted residues using the Debye-Scherrer method, identified the compounds MnAl₆, MgO and Mg₂Si in the 7075 alloy in the aged condition, the insoluble phase Mn₁₂Si₇Al₅ in the 6061 alloy in both the solution heat-treated and aged conditions. In the 2011 alloy the primary precipitate, CuAl₂, was extracted in the aged condition and the lattice parameters for this tetragonal compound were determined to bea=6.064 Å andc=4.874 Å: Metallic bismuth also was identified in the extraction from this alloy. Several lines, believed to represent an unknown ternary or higher compound, could not be identified.