Due to its low density and high strength, magnesium has increasing potential in the lightweight area, especially as a material for structural components. To address the corrosion problem, which is the main issue with using Mg alloys in the automotive industry, as well as to address wear problems, a new technique that uses an asymmetric potential pulse waveform to form nanocrystalline PEO (plasma electrolytical oxidation) coatings on Mg substrates, especially on sheet Mg plates, is developed in this study. The results of the analysis of PEO coatings on different sheet Mg alloy plates, which are characterized by electrochemical analysis methods including electrochemical impedance spectroscopy and potentiodynamic polarization are presented in this study. Furthermore, the coatings are characterized regarding their morphology and wear resistance, while varying the coating thickness by different processing times. A further improvement of the applied waveform by an on-top modification of the pulse signal leads to higher corrosion resistance as well as to a better performance in the tribological testing.

Increasing the application fields of magnesium by ultraceramic®: Corrosion and wear protection by plasma electrolytical oxidation (PEO) of Mg alloys

New Mg–Al based alloy sheet with good room-temperature stretch formability and tensile properties

The kinetics of dynamic recrystallization (DRX) of AZ31-0.5Ca magnesium alloy during warm rolling was studied. Isothermal compression tests were employed to evaluate the DRX in AZ31-0.5Ca. The results suggested the increase in fraction of DRXed grains as Zener-Hollomon parameter decreased, and the DRX started in earlier stages of the deformation.

Dynamic recrystallization behavior of AZ31-0.5Ca magnesium alloy during warm rolling

Twinning-detwinning behavior of E-form Mg alloy sheets during in-plane reverse loading

Improvement of strength and ductility synergy in a room-temperature stretch-formable Mg-Al-Mn alloy sheet by twin-roll casting and low-temperature annealing

The heterogeneity of both deformation and twinning behaviors through the thickness direction in E-form Mg alloy sheets was investigated via conventional Erichsen testing at room temperature (RT). The microtexture heterogeneity through the thickness direction of the E-form Mg alloy sheets deformed by different punch strokes (PSs) is discussed in terms of deformation twinning and de-twinning. The evolution of the microtexture, twin and KAM (kernel average misorientation) of E-form Mg alloy sheets deformed by different PSs was analyzed via electron back-scattered diffraction (EBSD) technique. A crystal plasticity finite element method (CPFEM) based on a random mapping (RM) scheme was used to simulate the heterogeneities of the strain/stress states of E-form Mg alloy sheets through the thickness direction during an Erichsen test. The evolution of the strain/stress that developed in E-form Mg alloy sheets during Erichsen testing was analyzed for different regions through the thickness direction under different PSs. EBSD analysis revealed that tension (TTWs), compression (CTWs) and double (DTWs) twins were the main deformation mechanisms in the upper portions. However, in the lower portions, a change in the sign of strain/stress components during Erichsen testing resulted in a significant formation of TTWs in the early stages and in a de-twinning of TTWs in the later stages.

Heterogeneity in deformation and twinning behaviors through the thickness direction in E-form Mg alloy sheets during an Erichsen test

Unraveling the formation mechanism of deformation bands in AA1100 alloy during plane forging and return-plane forging

In this study, sound workpieces made of interstitial-free (IF) steel were manufactured by performing up to 4 cycles without the occurrence of forging defects via the use of a new multi-axis diagonal forging (MADF-ver2) process at room temperature. The microstructure that was developed in the deformed specimens was experimentally analyzed and compared. As the number of cycles increased, the average grain size gradually decreased, and both the average misorientation angle and the fraction of high-angle grain boundaries (HAGBs) continued to increase. As the number of cycles increased, the change in average geometrically necessary dislocation (GND) density was insignificant due to the occurrence of dynamic recovery. The effects of microstructural factors on the hardness, yield strength, and total elongation of the deformed specimens were investigated. The ultrafine-grained structure formed by MADF-ver2 continuously increased the hardness and yield strength with increases in the number of cycles. On the other hand, total elongation was not dependent on the number of cycles, and this independence was mainly the result of insignificant changes in the average GND density due to the dynamic recovery that occurred throughout the specimen. 

Evolution of the microstructure and mechanical properties of interstitial-free steel during multi-axial diagonal forging

In this study, the deformation bands (DBs) in AA1100 after plane forging (PF) and return-plane forging (R-PF) during multi-axis diagonal forging (MADF) were observed using microtexture analysis. Typical texture components (plane-strain texture components) observed in face-centered cubic (FCC) materials deformed by plane-strain compression were developed in the PF specimen. Blurry bands with an orientation relationship of mainly LAGBs were developed in the deformed grains in the PF specimen. Slip trace analysis and Schmid factor (SF) calculations revealed the correlation between the blurry bands and the slip behavior. Regions of matrix and DBs inside the deformed grains of the R-PF specimen were distinguished mostly by their HAGBs. The heterogeneity of the Taylor factor (M) values that occurred within the blurry bands and their surrounding regions induced the development of the DBs in the R-PF specimen. The heterogeneities of the deformation behavior between the inside and the outside of the blurry bands that developed in the grains of the PF specimen during the R-PF were a direct reason for the generation of DBs in the deformed grains of the R-PF specimen. The transmission-EBSD (t-EBSD) technique revealed that the average misorientation angle inside the DBs was higher than that inside the matrix. 

Characterization of the deformation bands in AA1100 deformed by plane forging and return-plane forging

In this study, we investigated the detwinning phenomenon of in-plane compressed E-form magnesium (Mg) alloy sheet systematically using in situ tensile test combined with electron backscattered diffraction (EBSD) technique. Microstructure and microtexture evolutions were analyzed at different tensile strains during the in situ tensile test. The detwinning phenomenon in E-form Mg alloy was found to be linked to both twin boundary mobility and the interaction of their boundaries with dislocations. The pre-compressed sheet of E-form Mg alloy effectively accommodated the thickness direction strains generated during the in situ tensile test. The effect of detwinning on formability and mechanical behavior of the E-form Mg alloy was also examined. EBSD results indicate that most of the deformation twins formed during in-plane compression were removed when the load is reversed during the in situ tensile test.

Seong-Eum Lee

Papers

Heterogeneity in deformation and twinning behaviors through the thickness direction in E-form Mg alloy sheets during an Erichsen test

Unraveling the formation mechanism of deformation bands in AA1100 alloy during plane forging and return-plane forging

Evolution of the microstructure and mechanical properties of interstitial-free steel during multi-axial diagonal forging

Characterization of the deformation bands in AA1100 deformed by plane forging and return-plane forging

An Investigation of Detwinning Behavior of In-plane Compressed E-form Mg Alloy During the In Situ Tensile Test