Effect of thermo-mechanical alloying and ageing in AA2014 aluminium alloys after synthesized using graphite

Abstract

There is always a necessity to tailor new age materials for use in aircraft and automobile industries, and also in sophisticated fields at which resistance to elevated temperatures is of prime importance. To ensure the stability of high-strength levels of conventionally precipitation-hardened aluminium (Al) alloys, thermo-mechanical alloying and ageing treatment (TMAAT) was applied to AA2014 Al alloys. Essentially, AA2014 alloy was thoroughly decorated with fine Al dispersoids and precipitates by means of ball-milling and conventional ageing. Hence, using powder metallurgy methodology, powders of AA2014 alloy and graphite were mechanically alloyed (MA) for 7 h in a vertical attritor. The obtained powder mixture was then cold pressed into samples under the pressure of 800 MPa. To decorate the matrix with finely distributed $$\hbox {Al}_{4}\hbox {C}_{3}$$ phase particles (dispersoids), samples were systematically annealed (sintered) for a long time in a furnace system operating under a controlled atmosphere of argon at $$550{^{\circ }}\hbox {C}$$ . This temperature was found to form a ternary Al–Cu–Mg liquid phase in carbon-blended AA2014 alloy during sintering. However, the $$\hbox {Al}_{4}\hbox {C}_{3}$$ phase could not be observed. After subsequent homogenization and water quenching, all samples were age hardened at $$150{^{\circ }}\hbox {C}$$ for 46 h. Results confirmed that ordinary AA2014 alloy with $$\hbox {Al}_{2}\hbox {Cu}$$ precipitates over-aged normally as expected. In contrast, the material treated by MA had reinforcing $$\hbox {Al}_{4}\hbox {C}_{3}$$ particles together with $$\hbox {Al}_{2}\hbox {Cu}$$ precipitates. It was realized that this reinforced material did not soften and still retained its high peak hardness level even during prolonged over-ageing treatment. Consequently, it was apparent that TMAAT improved the strength, and therefore was promising for resistance to high-temperature exposure of the material.