Materials Science Forum Vol. 879

Abstract: The Al-1% Mg and Al-0.1% Mg alloys were both processed by high-pressure torsion (HPT) at room temperature. In the Al-1% Mg alloy, the hardness values in the disc centre area are lower than in the disc edge area after 1/2 and 1 turn, and the area of lower hardness values in the disc centre decreases as the number of turns increases from 1/2 to 1 turn. Finally, the hardness values are reasonably homogenous along the disc diameter as the number of turns increases to 5 and 10 turns. The Al-0.1% Mg alloy displays a different hardness evolution behavior: the hardness values in the disc centre are higher than at the disc edge 1/2 and 1 turn, and the area of higher hardness values decreases as the numbers of turn increases from 1/2 to 1 turn. The hardness values evolve towards homogeneity along the disc diameter after 5 and 10 turns. EBSD microstructure investigations in the Al-0.1% Mg alloy reveal that a few low-angle boundaries exist at the disc edge after 1/2 turn. It is suggested that the higher hardness values in the disc centre in the Al-0.1% Mg alloy are related to rapid recovery at the disc edge where the material is subjected to heavy straining.

Abstract: A new Mg-RE (rare earth) alloy was previously developed by micro-alloying method (RE< 0.4 wt.%), which achieves a high ductility and good corrosion resistance. In-situ tensile test via neutron and synchrotron diffraction were performed to investigate first the deformation behaviour; and second the texture evolution which can be related to the deformation mechanism, and finally to understand why the as-cast Mg-RE alloys show such a high tensile ductility.Preliminary results showed that a dominated basal fibre texture was gradually developed with the increase of tensile strain. However, before the sample was broken a (10.0) fibre texture showed a similar intensity to that in (00.2), which means more activations of the non-basal slip planes during tensile deformation. This could also contribute to a relatively high elongation of this new Mg-RE alloy at room temperature. Further discussion will be showed together with the microstructures.

Abstract: This paper shows how characteristic solidification temperatures, including rigidity temperature can be used to quantify the various feeding mechanisms that occur during solidification of AlSiMg alloys. In addition, the impact of Silicon, Magnesium and Strontium on the temperature intervals of various feeding regions have been analyzed.

Abstract: An Al-Zn-Mg-Cu high strength alloy ingot produced by Direct-Chill casting was used in this study. The distribution of porosity in the cross section of the DC ingot was investigated by the precision density method (Archimeds’ principle), also X-ray microtomography technique was used to quantitatively analyze porosities in typical positions. The pattern in the cross section as well as in the thickness and width direction was obtained. The results show that: in the cross section of the ingot, porosity was increasing gradually from the surface to the center of the ingot; porosity shows an overall escalating trend from the surface to the center of the ingot both in thickness direction and in width direction; porosity was closely related to the cooling rate in the ingot; oxide inclusions have an effect on the formation of porosity to some extent.

Abstract: A micro-scale interface strength evaluation technique is essential for evaluating cold-sprayed materials. A focused ion beam (FIB) micro strength test enables the micro-scale evaluation of the interface mechanical properties. However, this technique cannot be used to measure the strain in a specimen. This work discusses the possibility of strain measurement by combining this technique with image analysis in a newly designed test setup. Moreover, the micro stress-strain curve for cold-sprayed copper was obtained. This improved method enables us to measure stress with a precision of 5 MPa and strain with a precision of 0.015. It was determined that some local regions can deform plastically, which could not be determined with conventional micro-and macro-scale evaluation methods. These results proved that the coating is non-uniform, while also revealing various microstructure and mechanical properties.

Abstract: The Mg-Zn-Y alloy with long-period stacking ordered (LPSO) phase is known as attractive for automotive lightening engine components with strength at elevated temperature. On the other hand, it is considered that the thermal conductivity of magnesium alloys is lower than that of commercial aluminum alloys. Low thermal conductivity causes engine performance degradation. However, there is little study on the thermal conductivity of Mg-Zn-Y casting alloys. It is important study when we consider the application of high-temperature parts for engine components. Then we developed the Mg-Zn-Y casting alloys with strength at elevated temperature and good thermal conductivity. Our developed alloys have the fine LPSO phase with a net-like structure for higher strength and the pure magnesium matrix for better thermal conductivity. It is important that there is little or no solute element in the magnesium matrix for thermal conductivity. We accomplished these two good characteristics at the same time by optimizing the amount of zinc and yttrium contained in the Mg-Zn-Y casting alloys. Mg₉₆Zn₂Y₂ die-casting alloy had a good thermal conductivity of over 100 Wm^-1K^-1 at 473 K. This was almost identical to the thermal conductivity of heat-resistant aluminum casting alloys for conventional engine components.

Abstract: We carried out in situ x-ray diffraction measurements of magnetostriction in an Fe-18at%Ga alloy single crystal under magnetic fields. The sample studied here was a Goss-oriented square plate (dimensions: 10 mm × 10 mm × 1 mm height) cutting from as-grown single crystal ingot produced by the Czochralski method. In-plain magnetic fields were applied with various directions in this study. The influence of magnetic field direction on the stress/strain states was precisely analyzed by using our original x-ray single crystal stress/strain measurement method. As a result, applied field angle dependence of tri-axial magnetostriction states was successfully obtained. Thereby, we found that the singular anisotropic mechanical properties of this material play an important role for its magnetostriction properties.

Abstract: Silicon carbide (3C-β SiC) samples were irradiated with He ions of energy up to 30 keV and a fluence up to 10¹⁶/cm², to produce damage in the near-surface region. A duplicate set of He ion irradiated SiC samples, as well as undamaged SiC, were also irradiated with H₂⁺ ions of energy up to 20 keV and a similar fluence, to study the interaction of H species with pristine SiC and with He radiation-damaged SiC. Samples were annealed in steps of 200 K, from 473 K to 1273 K, and the retention of H and He were measured using elastic recoil detection analysis with 7.8 MeV C³⁺ ions, after each anneal step. Modification to the surface following irradiation is observed via Raman spectroscopy, which exhibits development of damage states such as disordered carbon and Si-Si peaks. Only minor changes in the H and He profiles were observed up to 1073 K, however after the 1273 K anneal the H and He profiles changed considerably, with a marked difference between samples irradiated only with He and those irradiated with He and H.

Abstract: Mg-Ni-Y alloy with composition ratio of 1 : 2 (Ni : Y) consisted of Mg, and 18R-type long period stacking ordered (LPSO) phases, whereas composition ratio of 1 : 1 (Ni : Y) consisted of Mg,14H-type LPSO and Mg₂Ni phases, respectively. After hot-rolling at 693K, strong basal texture parallel to the plane sheet was formed in the LPSO, and Mg phases. Tensile test was performed along rolling direction (R.D) from room temperature (R.T) to 573K. The Mg₉₈Ni₁Y₁, Mg₉₆Ni₂Y₂, Mg₉₄Ni₃Y₃, Mg₉₇Ni₁Y₂ and Mg₉₄Ni₂Y₄ rolled sheets exhibited 0.2% proof stress (σ_0.2) of 232MPa, 255MPa, 358MPa, 337MPa and 393MPa, and elongation (δ) of 6%, 5%, 7%, 15% and 7% at R.T, respectively. The σ_0.2 of the Mg-Ni-Y rolled sheet tend to increase with increasing of area fraction of the LPSO phase. After annealing at 773K for 0.6ks, the δ of Mg-Ni-Y rolled sheet tend to increase, while the σ_0.2 decreased due to randomization of the Mg phase by re-crystallization. The Mg-Ni-Y rolled sheets exhibited high σ_0.2 above 200MPa at 473K. Additionally, it was noted that σ_0.2 of the Mg₉₄Ni₂Y₄ rolled sheet exhibited 329MPa at 473K and 211MPa at 573K. Thus, the LPSO phase have high thermal stability and is attribute to strengthening of the Mg-Ni-Y alloy sheet at high temperature.

Abstract: The technological and metallurgical advancements of value-added niobium (Nb) microalloyed thermo-mechanical controlled process (TMCP) plate steels continue to be developed for more demanding end user requirements. The market demand for reduced fuel consumption and CO₂ emissions in the automotive and construction sectors have further increased the demand for these new and advanced higher quality Nb-bearing steel grades. Often, the transition from laboratory melted and TMCP hot rolled heats to the production scale requires some continuous casting, thermal and mechanical metallurgy adjustments from the laboratory results in order to accomplish proper industrial continuous casting and hot rolling processes. These advanced high strength steels are microalloyed with Nb, Mo and/or other elements which affect the austenite-ferrite transformation. Niobium enables achievement of substantial grain refinement when the plate is rolled with the proper reduction and thermal schedule. The effects of these microalloying elements on the continuous cooling transformation behavior must be carefully controlled during the reheating and rolling process to successfully achieve the desired mechanical properties. TMCP applications have been successfully developed in numerous product sectors with thickness exceeding 120 mm. Since the very fine grained microstructure improves toughness and increases the yield strength, this TMCP process enables the required tensile properties with the growing trend to leaner chemical composition designs (less than 0.10%C) and excellent toughness properties. The consequence of leaner chemical compositions, especially lower carbon content and lower carbon equivalent enhances mechanical properties, fabrication and weldability.