Effect of Carbon Nanotubes on Solution Treatment Temperature and Dissolution Characteristics of Precipitates in Al Alloy Produced by High-Energy Milling and Hot Extrusion

• Published in: Transactions of the Indian Institute of Metals 2019-10, Vol.72 (10), p.2687-2697
• Main Authors: Anas, N. S., Chandrasekhar, S. B., Dash, R. K., Rao, Tata N., Vijay, R.
• Format: Article
• Language: English
• Subjects: Aluminum base alloys; Carbon nanotubes; Chemical precipitation; Chemistry and Materials Science; Corrosion and Coatings; Dispersion strengthening; Dissolution; Extrusion coating; Hot extrusion; Magnesium; Materials Science; Mechanical alloying; Mechanical milling; Metallic Materials; Nickel; Precipitates; Solution heat treatment; Solution strengthening; Technical Paper; Tribology; X-ray diffraction
• ISSN: 0972-2815; 0975-1645
• DOI: 10.1007/s12666-019-01736-7

The present study discusses the effect of CNT on the solution treatment temperature for Al alloy (AA), i.e. Al–4.4Cu–0.5 Mg, Al alloy–CNT (AC) and Al alloy–Ni-coated CNT (ANC) composites fabricated by mechanical milling and hot extrusion. Differential scanning calorimetry indicated that dispersion of CNT in Al alloy increased the dissolution temperature of θ phase precipitates. X-ray diffraction (XRD) and scanning electron microscopy illustrated complete dissolution of θ phase in both AA and AC samples when solution-treated at 520 °C, whereas ANC sample exhibited the same behaviour at 500 °C itself. XRD patterns of ANC sample revealed the presence of an additional intermetallic Al 7 Cu 4 Ni phase, which remains undissolved even after the solution treatment at 540 °C. Utilisation of Cu atoms to form Al 7 Cu 4 Ni phase resulted in significant reduction in size and number density of θ phase in ANC. The hardness of AC and ANC samples was found to be higher compared to AA owing to dispersion strengthening by CNT and Al 7 Cu 4 Ni particles.