Investigation of Microstructure, Mechanical Properties and Residual Stress in Non-equal-Channel Angular Pressing of 6061 Aluminum Alloy

Proceedings of the Institution of Mechanical Engineers, Part L:

2021

In this research, the residual stresses distribution resulting from one of the severe plastic deformation methods called Constrained Groove Pressing in pure copper sheets has been studied experimentally and numerically. For this purpose, after the initial preparation of each sample, the mentioned process is applied to the samples up to three passes. After each pass, the residual stresses in these samples in both directions of their length and width have been measured experimentally. To measure the residual stresses in these samples, the contour method, which is a relatively new, effective, and accurate method in providing a two-dimensional residual stress map, has been used. The results indicate that the residual stresses on the surfaces of the samples are compressive and by moving towards the central layers of them, these stresses are converted into tensile residual stresses. The distribution of residual stresses along the length and width of the samples is reported to be relatively uniform. In another part of this research, numerical simulation of the Constrained Groove Pressing process in ABAQUS finite element software is discussed. In this simulation, Johnson–Cook model is used as a constitutive model. The average error of residual stress distribution between the simulation and contour method was about 18% which shown a good agreement.

Section: Introductionmentioning

confidence: 99%

Experimental and numerical study of the longitudinal and transverse residual stresses distribution in the constrained groove pressing process of pure copper sheets

Tavajjohi

Proceedings of the Institution of Mechanical Engineers, Part L:

2021

“…[7][8][9] In recent years, SPD techniques are widely applied in producing the UFG structures in bulk metallic alloys. [10][11][12][13][14] Equal channel angular pressing (ECAP), 15,16 high pressure torsion (HPT), equal channel angular rolling (ECAR), [18][19][20] constrained groove pressing, [21][22][23][24][25] non-equal channel angular pressing 26 and cyclic close die forging (CCDF) 27 are some of the SPD processes which have been recently investigated.…”

Section: Introductionmentioning

confidence: 99%

The effects of combined cyclic close die forging and aging process on microstructure and mechanical properties of AA7075

Moazam

Proceedings of the Institution of Mechanical Engineers, Part L:

2020

It is well known that applying severe plastic deformation methods on the precipitation hardenable aluminum alloys at room temperature is very difficult because of crack formation and segmentation of the specimen during the processes. In this study, several procedures were experimentally examined for performing the cyclic close die forging (CCDF) and improving the mechanical properties of AA7075. The experimental tests revealed that supersaturated solid solution of AA7075 after water quenching is formable for only about 5 min and performing the CCDF process in this limited time is possible. Optical and scanning electron microscopy and transmission electron microscopy were used to study the microstructure of the processed samples. It was observed that by applying two passes of CCDF, the grain size of the material reduced from 30 µm to about 200–300 nm. In addition, the X-ray diffractometer results demonstrated that Guinier–Preston zone picks of the processed samples are very weak and the equilibrium η-phase does not exist in none of the suggested procedures. Furthermore, it was found that by combining CCDF and aging processes according to the proposed procedures, the mechanical properties of the processed AA7075 were improved when compared with the AA7075-T6. To put it more clearly, micro-hardness, yield strength and ultimate tensile stress of the processed sample were improved as much as 38.6%, 25% and 23%, respectively.

“…Nowadays, the study of the effect of the SPD process on RS formation and distribution has become an interesting subject. In this field, several methods were used such as ring-core, 36 slitting, [37][38] contour, 35,39 hole-drilling, 40 etc. Although different techniques were developed to measure the RS, just a few methods are suitable for through-thickness measurement.…”

Section: Introductionmentioning

confidence: 99%

Improving the mechanical properties and reducing the residual stresses of AA7075 by combination of cyclic close die forging and precipitation hardening

Moazam

Proceedings of the Institution of Mechanical Engineers, Part L:

2020

As one of the major strengthening mechanisms, the precipitation hardening is used to enhance the mechanical properties of aluminum alloys. Based on the results of the residual stress measurement, after fast quenching, the core of the material is under tensile stress while the surfaces are under compressive residual stress. Distortion commonly happens during the machining of precipitation-hardened aluminum alloys due to the residual stresses created during the quenching step in the heat treatment process. In this study, the combination of cyclic close die forging and precipitation hardening was used to improve the mechanical properties and control the residual stresses of AA 7075, simultaneously. According to the results, a considerable level of residual stresses was developed in the sample after the quenching step. Performing the cyclic close die forging process immediately after the quenching step changed the pattern of the residual stresses and reduced them significantly. The reduction of the residual stresses after the first pass of cyclic close die forging was about 50%, while after two passes, the sample was almost fully stress relieved. Besides, the results of the microhardness and uniaxial tensile tests demonstrated the improvement of the mechanical properties of the processed samples when compared to the T6 condition. Also, in comparison to AA 7075-T6, the yield stress, ultimate tensile stress, and microhardness were increased by about 24%, 22%, and 48%, respectively.