Microstructural evolution and superplasticity of Al-5.8Mg-0.23Mn alloys processed by reciprocating extrusion

Abstract

This study developed the reciprocating extrusion method to refine the inclusions and grain structure of Al-5.8Mg-0.23Mn alloys to enhance their strength and superplasticity without prior homogenization treatment. Alloy cast billets were extruded with an extrusion ratio of 10:1 at 450 °C for one, five, or ten passes. The grain size was reduced to 4.6 m, and the coarse inclusions refined to 2 m, after ten passes. A subgrain structure was formed in the interior of the fine grains, indicating that dynamic recrystallization occurred during extrusion. In this study, dynamic recrystallization in the billet was repeatedly induced by a number of extrusion passes until a limiting grain size was obtained. Thereafter, dynamic recrystallization was no longer activated because grain boundary sliding, instead of dislocation gliding, accommodated the deformation strain required for extrusion. The alloys extruded in ten-passes extrusion were found to be stronger and more ductile than commercial Al-Mg alloys and showed improved superplastic behavior at 500 °C not only from low to high strain rate but also with a small flow stress of less than 30 MPa. These advantages demonstrate that reciprocating extrusion can produce Al-Mg alloys with improved mechanical properties making them good candidates for high-strain-rate superplastic forming.

Microstructure evolution in magnesium alloy AZ31 during cyclic extrusion compression

“…The two chambers are connected by a smaller diameter d m . The basic difference of the present CEC extruder among those of Richert and Richert [6] and Yeh and co-workers [8,14] is that the die is a solid die. During operation, the extrusion force F A and F B can be controlled by the test machine.…”

“…alloys fabricated by cyclic extrusion compression (CEC) technique which originally proposed by Richert and Richert [6]. On the other hand, previous studies on materials such as pure Al [6,7], Al alloys [8,9], Mg-15Al-1Zn [10], Pb-50 vol.% Sn alloys [11] revealed that CEC can refine grains, second phase structures and inclusions. Regarding the refining mechanism, Yeh et al [10,12,13] proposed that particle fragmentation, dynamic recrystallization and repeated mass flow during deformation refine the grains and inclusions.…”

Effect of process parameters on the macrostructure and defect formation in friction stir lap welding of AA5456 aluminum alloy

“…The Al-Mg alloys have been widely used in structural applications for the bodies of dump trucks, large tanks, pressure vessels, boats, and buildings since the alloy AA5456, as the group leader, was the strongest non-heat treatable alloy commercially available for welded structures, storage tanks, and pressure vessels [2][3][4]. As, the application of traditional welding processes to several aluminum alloys emerge a series of defects such as porosity, cavities and hot cracking, FSW could be considered as a suitable process to improve mechanical properties and eliminate disadvantages for joining of the 5XXX alloy series [5].…”

Microstructure and high tensile ductility of ZK60 magnesium alloy processed by cyclic extrusion and compression

“…Moreover, it is very suitable for refining grains of hard-to-deform metals such as magnesium alloys since it imposes three-dimensional compression stresses during processing [13]. In the past CEC has been successfully used to produce a variety of metallic materials with ultra-fine grain structures [9,10,[13][14][15]. However, the available information in the literature concerned with the microstructure vs. mechanical properties after CEC is still very limited.…”