The Influence of Heat Treatment and High Energy Ball Milling on the Density, Hardness, and Wear Behavior of Al 7150 Alloy via Hot Uniaxial Compaction

Rahman, Abdur; Haque, Serajul

doi:10.22068/ijmse.2618

Volume 19, Issue 3 (September 2022) IJMSE 2022, 19(3): 100-112 | Back to browse issues page

‎ 10.22068/ijmse.2618

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Rahman A, Haque S. The Influence of Heat Treatment and High Energy Ball Milling on the Density, Hardness, and Wear Behavior of Al 7150 Alloy via Hot Uniaxial Compaction. IJMSE 2022; 19 (3) :100-112
URL: http://ijmse.iust.ac.ir/article-1-2618-en.html

The Influence of Heat Treatment and High Energy Ball Milling on the Density, Hardness, and Wear Behavior of Al 7150 Alloy via Hot Uniaxial Compaction

Abdur Rahman

, Serajul Haque

Abstract: (5394 Views)

The effect of the milling time & ageing on the hardness, density, and wear characteristics of Al 7150 alloy specimens made via powder metallurgy has been studied. The different constituents of Al 7150 alloy were processed in a planetary ball milling set up with a BPR of 10:1 for 5 hours, 10 hours, and 20 hours. At 400 °C, the milled powders were subsequently hot compacted in a punch die setup. The hot-pressed specimens were solutionized initially, then aged artificially at 115 °C for 3, 6, 12, 24, 30, 45, 60, and 96 hours. The relative density was inversely proportional to the milling time. Microhardness tests showed a maximum VHN of 255 was measured for the 24 h aged T6 specimens produced from 20 h milled powders whereas the non-aged specimens, made from unmilled 7150 alloy powders showed a VHN of 40. However the samples showed a decline in microhardness beyond 24 h of ageing. Under various conditions of sliding distance and loading conditions, the samples subjected to T6 aging showed a reduced volumetric wear rate indicating the beneficial effect of artificial aging up to 24 hours. The volumetric wear rate gradually declined for the samples aged beyond 24 hours of aging. The HRTEM studies revealed a high density of uniformly scattered (MgZn₂) precipitates in the base matrix, as well as (MgZn₂) phases precipitating along grain boundaries. The presence of such second phase precipitates in the matrix improved the wear characteristics of the alloy matrix. The results showed that optimization of process parameters such as milling time, ageing as well as reducing the particle size of the base powders, the hardness and wear behavior of Al 7150 alloy may be improved.

Keywords: BALL MILLING, Al 7150, wear, aging, heat treatment

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1. According to XRD examination, the widening of the diffraction pattern could very well be attributable to the increase in the duration of milling from 0 to 20 hours, showing that perhaps the nano-crystalline state had been established as a result of HEBM. The emergence of MgZn₂ precipitates due to the combined application of heat and pressure was validated by XRD examination.
2. The relative density was inversely proportional to the increase in milling time which reduced the particle size from 0 to 49 nm after 20 h of milling of the base powders.
3. Owing to the precipitation hardening phenomena, the microhardness of all the specimens steadily enhanced after 3, 6, 12, and 24 hours of artificial ageing at 115°C. Peakage hardness was attained at 24 h of ageing, beyond which the microhardness (VHN) of all the specimens, regardless of particle size, began to decline. Overageing occurred after 96 h of ageing.
4. When compared to the other specimens, the T6 treated Al 7150 alloy made of milled powders of 49 nm size showed a superior microhardness of 255 VHN. This is due to the particle size reduction due to increasing the duration of milling as well as close packing of the powders under the influence of the simultaneous application of pressure and heat during hot pressing.
5. Pin on disc wear testing conducted under varying loads and sliding speeds showed the beneficial effect of artificial ageing in enhancing the wear behavior of the T6 treated samples.
6. The capacity of the T6 specimens to withstand the dry sliding wear loads throughout pin-on-disc wear testing can be attributed to the development of (MgZn₂) precipitates, which slowed dislocation movements.
7. The T6 sample’s HRTEM microstructure showed a high density of MgZn₂ precipitates dispersed evenly in the Al 7150 alloy matrix, the precipitates comprising of the metastable η′ phase, with lesser amounts of GP zones and the stable η phase were observed.
8. FESEM morphology revealed extensive damage on the wear specimen’s surface due to severe plastic deformation during wear testing, indicating poor wear resistance of the non-aged samples. A mixture of adhesive, delamination and abrasive wear modes was identified during FESEM analysis.
9. The current study concludes that by optimizing the process parameters such as milling time, ageing as well as reducing the particle size of the base powders, the hardness and wear behavior of Al 7150 alloy may be improved.

Type of Study: Research Paper | Subject: Casting and Solidification

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