On the effect of HPT processing conditions on relative density, mechanical properties and microstructural evolution of hot compacted AA6061– mathematical empirical and response surface approach

¹Mechanical Engineering Department, Unizah College of Engineering, Qassim University,  King Abdulaziz St., 51911, Kingdom of Saudi Arabia

²Department of Manufacturing Engineering Technology, College of Technological Studies,  P.O. Box 42325, Shuwaikh 76504, Kuwait

Adv. Mater. Lett., 2017, 8 (5), pp 620-628

DOI: 10.5185/amlett.2017.1402

Publication Date (Web): Apr 04, 2017

Copyright © IAAM-VBRI Press

E-mail: W.Nasr@qu.edu.sa

Abstract

A loading combination of hot compaction (HC) together with high-pressure torsion (HTP) was used to consolidate discs of AA6061 considering rotations up to 4 revolutions and loading pressure values of 1 and 3 GPa. Mathematical models were established to grasp the true functional interrelationships and variations in the resulting relative densities, mechanical properties, and micro-structural evolutions as affected by the HPT processing pressure and the imposed strain. Sequential iterative nonlinear regression procedures were employed to get the most suitable mathematical relationships that express the relationship between the variables under study.  The developed models were examined for its adequacy and significance by using ANOVA analysis as well as many other statistical criteria. Response surface and contour graphs were established for a better understanding of the true functional dependence and, for a quantitative assessment of the intended relationships. It was observed that uniformity of hardness distribution increased with increasing each of the equivalent strain (ε_ef) and the imposed pressure. A remarkable increase in the compressive strength of deformed discs has been observed. HPT processing produced a tri-model structure with micron scale grains and subgrains, and nano-scale substructure. 

Keywords

AA6061, high pressure torsion, ultrafine grained materials, nonlinear regression procedures, response surface methodology.