MICRO-HARDNESS EVOLUTION OF Al-ALLOY AA 3004, PROCESSED BY EQUAL CHANNEL ANGULAR PRESSING

Abstract

Equal Channel Angular Pressing (ECAP) is a very interesting method for modifying the microstructure in producing materials with ultrafine grain in sub-micrometer or nanometre range. Experiments demonstrate that these ultrafine structures may exhibit, by comparison with large -grained polycrystals, major differences in some fundamental properties. A nanostructured AA 3004 alloy was used to investigate the evolution of microhardness and microstructure on the cross-sectional plane X, after processing by ECAP at room temperature for up to six passes. The measurements show the average microhardness increases significantly after two passes with additional increases in subsequent passes. Microhardness values increase by more than two times after 6 passes. There is a reduction in grain size from of ~ 50µm in the initial condition to ~ 12 µm after 6 passes. The results also show that the microstructure and the microhardness evolve with increasing strain so that, after a total of 6 passes, the structure is almost homogenous throughout the cross-sectional plane of the billet.Keywords: Al alloy; SPD; ECAP; micro-hardness; homogeneity IntroductionExtensive studies of equal-channel angular pressing (ECAP) and other severe severe plastic deformation (SPD) techniques, over the past two decades [1][2][3] have established the processing techniques and have shown the possibility of producing ultrafine grain (UFG) structure in many metals and alloys. Grain size reduction is one of the most attractive ways of improving the mechanical properties of metallic materials. It is known that the strength of all polycrystalline materials is related to the grain size, through the Hall-Petch equation which predict an increase in yield strength (σ y ) with a decrease in grain size (d): σ y = σ 0 + kd -1/2 [4,5]. Several different SPD procedures are now available but the most popular appears to be Equal Channel Angular Pressing (ECAP), that was first proposed in the 80 s, by Segal. In processing by ECAP the sample is pressed through a die containing two channels equal in cross-section, intersecting at an angle φ that is generally close to 90 o (Fig. 1). Since the sample emerges from

Archives of Metallurgy and Materials

“…Earlier reports described the evolution of homogeneity in the alloy Al-6061, where after 6 passes negligible increase in the microhardness is observed [20,22]. However, in our previous work, we have reported that the microhardness (HV) of the alloy A3004 [24] and AA5754 [25] improved with the number of ECAP passes. Also, other authors reported similar results of grain refinement on alloy AA3104 achieved by a hard pressure torsion (HPT) [26,27].…”

“…The samples for ECAP treatment were sintered from AA3004 powder of 50 mm grain size in a shape of cylindrical rods with 10 mm in diameter. The preparation was a subject to different studies [16,24,25]. The AA3004 powder material before the sintering contained 97.8% A1, 1.2% Mg and 1% Mn.…”

“…The samples were inserted into the vertical channel of the die. Herein, the bending angle is Φ = 90° and the typical angle of the arch where two channels meet, Ψ = 20° [24,25]. In ECAP processing the sample is pressed through the vertical channel of the die.…”

New Approach In The Properties Evaluation Of Ultrafine-Grained OFHC Copper

“…Owing to these attractive features, a lot of experimental studies focused on the development of ECAP method have been performed in recent years [24][25][26][27].…”

Validation of parameters selection of aluminium busducts welding with micro-jet cooling by using Method of Fundamental Solutions

“…The most commonly used alloys for welded constructions are alloys 5052, 5154, 5454, 5083 and 6061. The best filler material for welding that alloys is 4043 (4XXX group) or 5356 (5XXX group) [4][5][6]. The choice of filler material in aluminum welding is an important factor influencing mechanical properties [7][8].…”