Effects of solidification, solution and aging processes on an AlCuNb alloy: thermal and microstructural analysis, microhardness, electrical resistivity and conductivity

• Published in: Journal of thermal analysis and calorimetry 2024-02, Vol.149 (3), p.953-966
• Main Authors: Azevedo, Hugo M., Mendes, Gabriel H., Rodrigues, Helder C., Rocha, Fernando S., Costa, Thiago S., Moreira, Antonio L., Rocha, Otavio L.
• Format: Article
• Language: English
• Subjects: Aging; Aging (metallurgy); Analytical Chemistry; Chemistry; Chemistry and Materials Science; Cooling rate; Differential scanning calorimetry; Electrical resistivity; Eutectic alloys; Grains; Heat treating; Heat treatment; Ingot casting; Inorganic Chemistry; Macrostructure; Measurement Science and Instrumentation; Microhardness; Microstructural analysis; Microstructure; Physical Chemistry; Polymer Sciences; Solid solutions; Solidification; Thermal analysis; Thermodynamic properties
• ISSN: 1388-6150; 1588-2926
• DOI: 10.1007/s10973-023-12739-4

This paper analyzes the effect of both solidification and heat treatment process on microstructure, microhardness, electrical resistivity and electrical conductivity ( ρ and σ ) in an Al–3Cu–5Nb alloy (mass/%). In this sense, an unsteady-state horizontal solidification experiment was carried out using a water-cooled solidification device and as-cast samples were subjected to various T6-type heat treatment conditions. The solidification thermal parameters investigated were the growth and cooling rates ( V L and T R ), and those of the thermal treatment were the temperatures and times in the solution and aging stages. Techniques by optical and scanning electron microscopy differential scanning calorimetry (DSC) and X-ray diffractometry (XRD) were applied for microstructural and thermal analysis. The DSC results showed the plateau corresponding to the beginning and end of the formation of the Al-rich solid solution (Alα), indicated by the T Lα and T S /eutectic temperatures of the alloy (~ 645 °C and ~ 530 °C). An increase in the HV values with the application of the T6-heat treatment in the as-cast samples was observed for all assumed conditions and the best condition found was for 500 °C/3 h of solution, and 155 °C/5 h for the aging in which the hardness increased from 61.4 to 90.33 HV, equivalent to the increase of ~ 47%. It was observed that macrostructure consisting of columnar grains favor electric current flow contributing to the decrease of ρ , as a consequence increased σ . For the total length of the ingot, the electrical conductivity increased from 23.8 × 10 6 S m −1 in the solidified conditions to 40.1 × 10 6  S m −1 (~ 68.5%) in the T6 conditions equal to 490 °C/3 h and 155 °C/3 h in the solution and aging stages, respectively, as well as higher σ values were found in the region formed by columnar grains in which higher V L and T R values and lower secondary dendritic spacing ( λ 2 ) were obtained.