Influence of processing on microstructure and mechanical properties of magnesium alloy AZ91

This paper deals with differences of mechanical characteristics and fracture surface morphology of AZ91 magnesium alloy in extruded state and after subsequent equal channel angular pressing (ECAP). According to the results, the tensile properties were not controlled by grain size only as values of the tensile strength and 0.2 proof stress were similar for both alloys despite having average grain size 15.9 μm for the extruded alloy and 1.2 μm for the ECAPed alloy. In contrast, microhardness seemed to be dependnt solely on the grain size. Fractographic analysis has shown changes in the damage mode from quasi-cleavage fracture in extruded state to rather ductile fracture with dimple morphology in exECAPed state during tensile loading.

Changes in mechanical properties of as-cast magnesium alloy AZ91 after equal channel angular pressing

This paper deals with differences in mechanical characteristics of AZ91 magnesium alloy in the as-cast state and after the subsequent equal channel angular pressing (ECAP) and with measurement of local microhardness. According to the obtained results, the tensile properties increased by a factor of two due to the ECAP procedure.  The proof stress, σ0.2, increased to 160 MPa and the ultimate tensile strength, σUTS, to 321 MPa. The local microhardness of ECAPed alloy varied between 70 and 91 HV 0.025 due to microstructural bimodality.

EBSD ANALYSIS OF PHASE COMPOSITIONS OF TRIP STEEL ON VARIOUS STRAIN LEVELS

Flat test bar made of TRIP steel was sequentially strained in tension. Eeach deformation step was made on a predefined strain level in which the phase composition was measured using EBSD; the analyses were made ex-situ exactly in the same area of 30x30µm. Retained austenite (RA) was present in the form of elongated grains (plates) and roughly equiaxial ones. The RA content was initially 14.5% and decreased with imposed strain down to approximately 5% in selected strain range from 0% to 10%. This is in agreement to some extent with outcomes of both in-situ and ex-situ experiments presented by other authors, the difference beeing supposed either in data clean up or in variation in micriostruct ure of particular steel. Kernel average misorientation method was confirmed as useful tool to discern bainite and grainy ferrite in lightly deformed specimen. Problem arose in distinguishing between martensite and deformed ferrite at higher deformation levels because of high dislocation density and/or lattice distortion in both components. The ferrite and retained austenite fraction were analysed with sufficient accuracy; martensite fraction was established with high degree of uncertainty

Thermal stability of magnesium alloy AZ91 prepared by severe plastic deformation

This paper deals with the thermal stability of ultrafine-grained alloy AZ91 prepared by means of ECAP (Equal Channel Angular Pressing) method. Annealing experiments were conducted isochronally for 30 minutes in the temperature range of 220 to 400 °C in argon atmosphere. EBSD (Electron Backscatter Diffraction) method was used to image the changes in microstructure due to increased temperature

Microstructural changes of ECAP-processed magnesium alloy AZ91 during cyclic loading at different stress-amplitude levels

Microstructural changes of magnesium alloy AZ91 after fatigue loading in the EX-ECAP state were evaluated using EBSD. It was found that both the number fraction of low-angle boundaries and parameter KAM decreased after the testing at a stress amplitude of 160 MPa but started to increase with the increasing stress amplitude. This behaviour can be explained with a mutual influence of dislocation accumulation (which is stronger with a higher stress amplitude) and dynamic softening (which is weaker with a decreasing number of cycles/cycles to failure). The average grain size remained almost unchanged except at a stress amplitude of 180 MPa, which could have been caused by certain conditions allowing an ideal development of both mentioned phenomena

Selective Laser Melting Strategy for Fabrication of Thin Struts Usable in Lattice Structures

This paper deals with the selective laser melting (SLM) processing strategy for strut-lattice structure production which uses only contour lines and allows the porosity and roughness level to be managed based on ombination of the input and linear energy parameters

Influence of pre-strain on cyclic creep of copper

Cyclic stress component can either accelerate of decelerate the cyclic creep of copper loaded with a high mean stress, according to details of the start-up procedure of a fatigue test

Influence of processing on microstructure and mechanical properties of magnesium alloy AZ91

This paper deals with differences of mechanical characteristics and fracture surface morphology of AZ91 magnesium alloy in extruded state and after subsequent equal channel angular pressing (ECAP). According to the results, the tensile properties were not controlled by grain size only as values of the tensile strength and 0.2 proof stress were similar for both alloys despite having average grain size 15.9 μm for the extruded alloy and 1.2 μm for the ECAPed alloy. In contrast, microhardness seemed to be dependnt solely on the grain size. Fractographic analysis has shown changes in the damage mode from quasi-cleavage fracture in extruded state to rather ductile fracture with dimple morphology in exECAPed state during tensile loading