Vacancy-Type Defects Study on Ultra-Fine Grained Aluminium Processed by Severe Plastic Deformation

Abstract

Vacancy-type defects play an important role in the metal materials deformed by severe plastic deformation (SPD). The present work use positron annihilation lifetime spectroscopy (PALS) to test the vacancy-type defects in aluminium alloys processed by equal channel angular pressing (ECAP) and accumulative roll bonding (ARB). ECAP at room temperature and cryogenic temperature was conducted to AA1050 and ARB with 200 C preheating was conducted to AA1050 and AA6061 to produce laminated AA1050 sheets, AA6061 sheets and AA1050/AA6061 composites. High fraction of vacancy-type defects were detected in all the deformed samples. Vacancies associated with dislocations and bulk mono-vacancies have been identified in RT-ECAP deformed samples. Three types of vacancy-type defects, vacancies associated with dislocations, bulk mono-vacancies and bulk di-vacancies, have been identified in the CT-ECAP processed samples. The ARB process is more efficient in grain refinement and strengthening. However, the accumulation of vacancytype defects in ARB deformation seems less efficient. Vacancies associated with dislocations are the major vacancy-type defects for ARB processed AA1050 sheets but there exist some bulk mono-vacancies. However, most of the vacancy-type defects in the ARB processed AA6061 are vacancies associated with dislocations. A very small fraction of bulk mono-vacancies can be extracted but it is so small that it can be neglected. The lifetimes of ARB processed AA1050/AA6061 composites are generally in between the values of AA1050 sheets and AA6061 sheets. Voids were not detected in neither of the samples. ABSTRACTVacancy-type defects play an important role in the metal materials deformed by severe plastic deformation (SPD). The present work use positron annihilation lifetime spectroscopy (PALS) to test the vacancy-type defects in aluminium alloys processed by equal channel angular pressing (ECAP) and accumulative roll bonding (ARB). ECAP at room temperature and cryogenic temperature was conducted to AA1050 and ARB with 200 C preheating was conducted to AA1050 and AA6061 to produce laminated AA1050 sheets, AA6061 sheets and AA1050/AA6061 composites. High fraction of vacancy-type defects were detected in all the deformed samples.Vacancies associated with dislocations and bulk mono-vacancies have been identified in RT-ECAP deformed samples. Three types of vacancy-type defects, vacancies associated with dislocations, bulk mono-vacancies and bulk di-vacancies, have been identified in the CT-ECAP processed samples. The ARB process is more efficient in grain refinement and strengthening. However, the accumulation of vacancy-type defects in ARB deformation seems less efficient. Vacancies associated with dislocations are the major vacancy-type defects for ARB processed AA1050 sheets but there exist some bulk mono-vacancies. However, most of the vacancy-type defects in the ARB processed AA6061 are vacancies associated with dislocations. A very small fraction of bulk mono-vacancies can be extracted but it is so small t...

An Investigation of Interface Bonding of Bimetallic Foils by Combined Accumulative Roll Bonding and Asymmetric Rolling Techniques

“…A high-purity Al alloy and a supersaturated Al-0.3 wt pct Sc alloy were processed by accumulative roll bonding (ARB) to generate 0.5-mm gage sheets consisting of alternating layers of Al and Al(Sc) by Quadir et al [3] In these products, the bands in the Al(Sc) layers were observed to be more refined than those in the Al layers. Su et al [4] studied the microstructure and mechanical properties of a 1.5-mm-thick AA1050/ AA6061-laminated composite processed by ARB and observed grain refinement in both the AA1050 and AA6061 layers. The AA1050 layer was seen to be coarser and has more equiaxed microstructure than the AA6061 layer after the second ARB pass.…”

“…They were rolled with a reduction of 50 pct at 473 K (200°C). [4] The 1.5-mm-thick composite sheets were subsequently subjected to three AR passes using a multi-function rolling mill with dry friction [15] at different roll speed ratios until the thickness reduced to about 0.1 mm. The rolling mill had 120-mmdiameter rolls, independently driven by two 5.5 kW motors.…”

Microstructure and Mechanical Properties of AA5005/AA6061 Laminated Composite Processed by Accumulative Roll Bonding

“…Many studies have been carried out in this area. [8][9][10][11][12][13][14][15] Al/Cu, [8] Cu/Ag, [9] Cu/ Zr, [9] Al/Ni, [10] Al/Mg, [11,12] Fe/Cu, [13] and some other laminated composites have been produced by ARB.…”

Ultrafine grained AA1050/AA6061 composite produced by accumulative roll bonding

“…For the composite produced by ARB of dissimilar starting materials, the two materials certainly obtain different properties after ARB deformation. It is reported that the two layers in the composite have different microstructures and different mechanical properties measured mostly by hardness tests in separate layers [5,8,[14][15][16]. Although few studies have been done, the strength of the composite can be predicted by the rule of mixture [9].…”