Microstructure and Mechanical Properties of Mg-2.5%Tb-0.78%Sm Alloy After Ecap and Ageing

Abstract

The influence of ageing and Equal Channel Angular Pressing (ECAP) on the microstructure and mechanical properties of Mg-2.5%Tb-0.78%Sm alloy has been examined. The microhardness changes during ageing at 200• C show a slight increase. The aged microstructure at maximum hardness contains Mg 12 (Tb,Sm) -metastable β' phase of size about 2-10 nm as dispersed precipitates. The orientation relationship between β' phase and the matrix was found as follows: (0001) M g 110 β , 2110 M g [116] β . The ECAP passes were performed by two procedures: "I" -four passes at 350• C; "II" -one pass at 370• C, second pass at 340• C and third pass at 310• C. The grain size was reduced about 200 times as a results of ECAP process according "I" and "II" procedure. The grain refinement by ECAP improves significantly the compression yield strength and hardness. The Hall-Petch relationship was confirmed basing on microhardness measurements and the grain size after ECAP. The Mg 24 (Tb,Sm) 5 and Mg 41 (Sm,Tb) 5 particles smaller than 150 nm are located mainly at grain and subgrain boundaries and they prevent grain growth during ECAP processing. The microstructure evolution during ECAP can be described as dynamic recovery and continuous and discontinuous dynamic recrystallization.Keywords: magnesium alloys with rare earth metals, ECAP, microstructure, ageing, mechanical properties W pracy przeprowadzono badania mikrostruktury i właściwości mechanicznych stopu Mg-2,5%Tb-0,78%Sm po procesie starzenia oraz po odkształceniu plastycznym metodą ECAP. Starzenie stopu w temperaturze 200• C powoduje niewielki wzrost mikrotwardości. Mikrostruktura stopu starzonego o maksymalnej wartości twardości zawiera metastabilne drobnodyspersyjne wydzielenia Mg 12 (Tb,Sm) -β' o wielkości 2-10 nm. Roztwór stały α-Mg wykazuje następujące zależności krystalograficzne z wydzielonymi cząstkami β': (0001) αM g 110 β , 2110 αM g [116] β . Odkształcenie plastyczne metodą ECAP przeprowadzono stosując dwie procedury: "I" -cztery przejścia w 350• C, "II" -pierwsze w 370• C, drugie w 340• C i trzecie przejście w 310• C. Po procesie ECAP, dla obu procedur, nastąpiło dwustukrotne zmniejszenie wielkości ziarna. Zmniejszenie wielkości ziarna uzyskane metodą ECAP znacząco poprawia twardość oraz granicę plastyczności przy ściskaniu. Stwierdzono zależ-ność Halla-Petcha pomiędzy wartościami mikrotwardości oraz wielkości ziaren uzyskanymi w wyniku odkształcenia metodą ECAP. Cząstki Mg 24 (Tb,Sm) 5 i Mg 41 (Sm,Tb) 5 mniejsze niż 150 nm wydzielone na granicach ziaren i podziaren zapobiegają ich wzrostowi podczas procesu ECAP. Zmiany mikrostruktury zachodzące podczas procesu ECAP można opisać procesami dynamicznego zdrowienia oraz dynamicznej rekrystalizacji.

Characterization of defect microstructure in MgRE (RE=Ce, Nd) alloys after processing by high-pressure torsion using positron annihilation spectroscopy and a high resolution X-ray diffraction

“…Besides the application of non-conventional deformation techniques, RE additions like Ce and Nd were found to randomize the texture and alter recrystallization processes [7]. Indeed, individual RE elements have been used as alloying additions for more than three decades [8].…”

Comprehensive Research of FSW Joints of AZ91 Magnesium Alloy

“…At the same time, Mg has a very low density, i.e., about 33.6% lighter than Al and Ti, and 75% lighter than steel [2]. Mg is strengthened by additives [3][4][5], heat, and plastic treatment [6], e.g., ECAP technology [7,8]. Numerous alloys are formed based on a Mg matrix, and the most frequently tested magnesium alloys include AZ31, ZE41, AZ61, AM60, AZ61, AZ80, and AZ91 [9][10][11][12][13][14][15][16][17].…”

Archives of Metallurgy and Materials

“…Papers also shown the effects on the stress-strain curves, plastic flow, hardness, for this type of materials etc. Particularly interesting seem to be all the is-sues related to the impact of manufacturing process parameters, especially as regards the more advanced techniques like HP-HT (High Pressure-High Temperature) [10,11], FAST/SPS (Field Assisted Sintering Technique/Spark Plasma Sintering) [12], SHSB (Self Propagating High Temperature Synthesis in Bath) [13][14][15][16], ECAP (Equal-channel angular pressing) or KoBo [12,[17][18][19][20], FSP (Friction Stir Processing) [21][22][23], on changes in hardness, the waveforms of related curves, and other mechanical properties. The paper presents the results of studies regard to influence of manufacturing process parameters on the physical properties, hardness, plastic flow and shape of the stress-strain curves of the AISI 316L/TiB 2 /2p composite.…”