Name, gr 27
Report on “Precipitation Hardening of Al Alloys”
4th March 2013
Actions that we carried out:
Heating the samples of alloy Al/3%Cu (~520˚C)
Saturating – cooling the samples in the cold water.
Annealing (~250˚C) each of the samples (different time for each specimen).
Measuring the hardness by Vickers method. The measurements were conducted under the 5 kgf load and with we used a 136° pyramidal diamond indenter that forms a square indent.
Results:
| how long the sample was annealing [min] | measured hardness – Vickers hardness test | the arithmetic mean | standard deviation |
|---|---|---|---|
| 0 | 81.3/86.2/86.5 | ~84.7 | ~2.92 |
| 5 | 87.6/93/84.1/79.4/79.1 | 84.64 | ~5.85 |
| 20 | 96.1/106/112/97.7/98.4/98.4 | ~101.4 | ~6.22 |
| 35 | 115/103/105/105/111/115 | 109 | ~5.37 |
| 50 | 110/119/110/114/105/113 | ~111.9 | ~4.71 |
| 65 | 122/123/126/123 | 123.5 | ~1.73 |
The hardness of metal material is increasing with ageing time but, in fact, only to some time when it reaches its maximum (then, it can get even lower). That is because the microstructure of the material is changing. The more measurements we make, the better (and closer to the truth) the results are.