Study of the Effect of Ageing on Mechanical Properties of AA6061 Aluminium Alloy Used in Local Manufacturing

This study investigates the effect of artificial ageing parameters on the mechanical properties of AA6061 aluminium alloy, a material widely used in the fabrication of structural components, bus body frames, and light machinery parts in Nigeria's manufacturing sector. Understanding the precipitation hardening response of AA6061 is essential for local manufacturers in Nnewi, Anambra State, South East Nigeria, where artisan fabricators often process aluminium alloy components without standardised heat treatment protocols. Solution heat treatment is performed at 530 degrees Celsius for 1 hour followed by water quenching, and ageing is conducted at temperatures of 150, 170, 190, and 210 degrees Celsius for durations of 1, 2, 4, 8, and 16 hours. Vickers hardness, tensile strength, and yield strength are measured at each condition. Microstructural evolution is examined by optical microscopy and transmission electron microscopy to identify precipitate phases. Findings confirm a classic age-hardening response, with peak hardness occurring at 170 degrees Celsius after 8 hours (T6 condition), yielding a hardness of 107 HV and tensile strength of 305 MPa. Overageing at 210 degrees Celsius reduces hardness by 22 percent compared to peak conditions, attributed to coarsening of MgSi precipitates. The study provides practical ageing guidelines for Nigerian manufacturers processing AA6061 components. Keywords: AA6061, age hardening, mechanical properties, precipitation hardening, aluminium alloy.