Effect of atmosphere and heating mode on sintering of 6711 and 7775 alloys

Abstract

The current study examines the effect of sintering atmosphere and heating mode on the densification, microstructure, phase analysis and properties of Al–1Mg–0·8Si–0·25Cu (6711) and Al–7Zn–2·5Mg–1Cu (7775) alloys. The compacts were heated in conventional and 2·45 GHz microwave sintering furnaces under vacuum, N₂, Ar and H₂ at 630°C. Both alloy compacts coupled well with microwaves and underwent rapid heating (∼22°C min⁻¹). The overall processing time was reduced to about 55–58% through microwave sintering. Microwave sintering resulted in greater densification for 6711 alloy under vacuum followed by N₂. In contrast, 7775 alloy resulted in poor densification under all atmospheres as compared with conventional sintering. For all compositions and atmospheres, microwave sintering resulted in microstructural inhomogeneity with the absence/presence of a lower amount of intermetallic phases. This has been correlated with lesser time available for the diffusion of alloying elements into the Al matrix. The conductivity, hardness and corrosion properties of both compacts improved depending upon heating mode and atmosphere.

Keywords:

• 6711 and 7775 alloys
• Microwave sintering
• Atmosphere effect
• Densification
• Microstructure
• Properties

The authors would like to thank Mr Jessu Joys of AMPAL Inc., Palmerton, USA for providing the 6711 and 7775 aluminium alloy powders for the present study. This study was conducted under the Networked Center for Microwave Processing of Metal–Ceramic Composites funded by the Indo–US Science and Technology Forum (IUSSTF), New Delhi, India.