Question

What is the typical impact energy value of the material for 3 different heat treatments (any). Put some microstructures and discuss the impact energy differences . For alluminium 6061

Answer 1

Aluminum alloy 6061 (AA6061) is produced through precipitation hardening aluminum alloy contains Mg (0.8-1.2 wt.%) and Silicon (0.4-0.8 wt.%) as its major alloying elements. It is an age harden-able alloy, which means the mechanical properties was mainly controlled by the hardening precipitates that contained inside materials

Impact Energy values of Aluminium 6061 for different heat treatment conditions are

(i) Annealing:

Annealing of Aluminium / Aluminum 6061 alloy can be performed at 775°F for 2 to 3 hrs followed by controlled cooling at 10 to 260°C (50 to 500°F) per hour, and then quenching in water.

Typical impact values obtained are in the range of 33-36 J/m2.

(ii) Quenching:

Quenching is carried out in water medium after annealing.

Typical impact values obtained are in the range of 35-38 J/m2.

(iii) Ageing:

Aging of Aluminium / Aluminum 6061 alloy can be performed at 177°C (350°F) for 8 hrs. It is then cooled in air.

Typical impact values obtained are in the range of 42-46 J/m2 obtained at 160 oC.

The differences in the impact values of the specimen can be attributed to different heat treatments. Annealing is a great heat treatment to improve toughness of Al 6061 alloy. It was found in literature that, after 4 hours of annealing, there is almost 11% improvement in the impact strength. The increase can be related to the uniform microstructure that allows for excellent ductility and workability. Quenching allowed for increase in impact strength of Al 6061 alloy. The reason is due to low viscosity of water, which induces rapid cooling rate. Ageing also improves impact strength of aluminium and its alloys. Some literature states an increase of 61% in impact values compared to as-received sample. The reason is that during ageing, some of alloy's compounds precipitate out of the solution and end up at the grain boundaries to increase strength by interfering with slip planes. This means more energy is needed for the material to fracture. Thus, stiffer materials will have higher impact resistance.

For microstructures, i didn't get sufficient information.