The microstructural homogeneity, hardness and tensile strength of aluminium alloy 5083, with and without copper shielding (CS), processed by equal-channel angular extrusion (ECAE) are investigated in this work. The two opposite longitudinal faces of the rectangular billets are shielded with copper sheets of various thicknesses (1·0, 1·5, 2·0 and 2·5 mm) and ECAE’d at room temperature in route A (no rotation of billet) up to four times. The required extrusion load is drastically reduced due to the smaller coefficient of friction between the CS and channels of the steel die. The shielded copper reduces the effect of the dead metal zone and microcracks and improves strain uniformity in the extruded alloy. The hardness and tensile strength of the extruded alloy with CS are increased extensively due to newly formed submicron-sized grains in the homogeneous structure. Also, the ductility of ECAE’d alloy with CS is higher compared to that of the alloy extruded without shielding. It is noticed that the increase in the thickness of CS does not have a noteworthy effect on the structural and mechanical behaviour of the extruded alloy.

The purpose of the present study is to investigate the effect of Cu casing and wall thickness of the drilled copper bars on uniform distribution of imposed stain in terms of structural homogeneity and distribution of micro-hardness in the severely deformed AA 5083 after equal channel angular extrusion (ECAE). In this study, AA 5083 cylindrical inserts of 6 mm, 8 mm and 10 mm diameter with 100 mm length are tightly inserted in the 16 mm square copper bars having the respective diameter holes. The square cross sectioned AA 5083 billets of 16 mm × 16 mm and 100 mm length are also considered as feedstock. The longitudinal surfaces of the bimetallic metals are polished and annealed at 530 °C for 1 h and then processed by ECAE up to four passes in route A (same sense after every pass without any rotation) at room temperature using a die with square cross-sectioned channels having channel intersection angle (ϕ) 105° and outer corner angle (Ψ) 30°. The initial grain size of 60 µm has been greatly refined and the ultrafine grains of the sizes in the range of 400-700 nm are formed in the extruded AA 5083 inserts after the four passes. The microhardness of extruded AA 5083 significantly increased from 69 to 134 VHN, 132, 176 and 157 respectively for the square billets without Cu casing and cylindrical inserts with the diameters of 6, 8 and 10 mm covered with Cu casing after the four passes. The variations in the microhardness measurements at different regions on the sectioned surfaces are also investigated in this study. The requirement of pressing force is very significantly reduced by using copper casing which is having more ductile nature and the frictional forces between the copper and steel die are very less as compared to the Aluminium and steel. The chances of formation of dead metal zone are avoided by filling the corner gap by cooper metal during the ECAE process. The uniform distribution of strain imposed on the severely deformed billets develops the homogeneous ultrafine grain structure and significantly improves the micro-hardness of the processed material.

The microstructural evolution and mechanical behaviour of semicircular AA 5083 billets subjected to equal channel angular extrusion (ECAE), without and with copper casing (CC), are investigated in this work. The semicircular billets, circumferentially covered with and without CC, are extruded up to three passes in route A at room temperature. Even the coarse grain structure of the initial material is significantly refined, the microcracks and the structural defects were observed in the billets extruded without CC due to non-uniform strain distribution. The use of CC on the circumference of the semicircular billets reduces the dead zone effect on the structural homogeneity and minimises the formation of microcracks on the outer periphery of the extruded material. The uniform distribution of the effective strain imposed on the billets ECAE’d with CC enhances the development of equi-axed ultrafine grains at low pressing loads. The newly formed ultrafine grains with a size of few hundreds of nanometres significantly increase the mechanical properties of the ECAE’d AA 5083 with the CC. The obtained results were in good agreement with the earlier reports in which ECAE was carried with back pressure arrangement.

No abstract

In the present investigation the influence of two stages artificial ageing, 1st stage at 160°C followed by 2nd stage at 140°C on microstructure and mechanical properties of LM 25 alloy was studied. It is observed that the microstructure changed under the influence of two stages ageing. It is also observed that the decrease in ageing temperature in the second stage, increases mechanical properties of the alloy. The tensile strength of the alloy in single stage ageing at 160°C is studied and compared with two stages ageing.