Abstract
In the current study, an effect of cryogenic treatment on the ageing of a B₄C particulate reinforced 7075 aluminium alloy was investigated to identify changes in hardness with respect to ageing time. To achieve this, first, 10, 15, and 25 % by weight B₄C particulate containing 7075 Al composite specimens were produced by hot pressing of Al, Cu, Zn, and Mg elemental powders. Next, cryogenic treatment and multiple steps of tempering were adapted to several samples. Such as, after solutionizing at 470 °C and sub-zero treatment at –146 °C, successive intervals of artificial ageing at 120 °C for different time periods were applied. During the heat treatment, hardness values were measured after each interval. Findings reveal that, particularly after solutionization, cryogenic treatment before ageing yields high hardness values. However, the hardness of the composite material exceeds this level during ageing treatment, mainly after long ageing times.

Key words
B₄C particles, aluminium composite, sub-zero treatment, cryogenics, ageing

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