Goroh Itoh

Hydrogen emission at grain boundaries in tensile-deformed Al-9%Mg alloy by hydrogen microprint technique

Abstract In recently years, environmental problems, such as global warming and exhaustion of fossil fuels, have grown into serious problems. In the automakers, the development of the fuel cell vehicles using hydrogen as clean energy has been paid attention to. Aluminum alloys have already been applied to a liner material of a high-pressure hydrogen tank for fuel cell vehicles. However, the behavior of hydrogen in aluminum alloys has not been clearly elucidated yet. Therefore, it is necessary to analyze the hydrogen behavior in aluminum alloys. Hydrogen microprint technique (HMPT) has been known as an effective measure to investigate the hydrogen behavior. In the present study, the emission behavior of internal hydrogen on a tensile-deformed Al-9%Mg alloy was investigated by HMPT at room temperature. As a result, the hydrogen was emitted at some grain boundaries.

Effect of Cr and Zr Dopes on Hydrogen Behaviour in Rapidly Solidified Aluminium Foils

Hydrogen (H) behaviour in materials was investigated in rapidly solidified (RS) foils of pure aluminium (Al), Al-0.4 Cr and Al-0.25 Zr alloys (at %) by means of thermal desorption spectroscopy (TDS). In addition, Al-0.25; 0.3 Zr alloys were examined with respect to microstructure and its instability during the thermal process using SEM and microhardness measurements. The effect of dopes and heating rate on H desorption was summarized. The lowest energy desorption is attributed with significant thermal desorption peak which temperature was found is correlated with sample composition.

Effect of Rapid Solidification Processing on Hydrogen Behaviour in Aluminium

Thermal desorption spectroscopy (TDS) technique has been used to study hydrogen behaviour in rapidly solidified (RS) aluminium (Al) both as-cast and exposed to humid air (HA). The surface morphology of the foils was studied through atomic force microscopy (AFM). Analysis was made of the effect of rapid solidification processing (RSP) on H/microstructure interactions, including investigation of alloying element (0.05 at % Ti) influence on H trapping in Al.

The Role of Cr in H Desorption Kinetics in Rapidly Solidified Al

Hydrogen desorption kinetics for rapidly solidified high purity Al and Al-Cr alloy foils containing 1.0, 1.5 and 3.0 at % Cr were investigated by means of thermal desorption analysis (TDA) at a heating rate of 3.3°C/min. For the first time, it was found that oxide inclusions of Al2O3 are dominant high-temperature hydrogen traps compared with pores and secondary phase precipitates resulted in rapid solidification of Al and its alloys. The correspondent high-temperature evolution rate peak was identified to be positioned at 600°C for high purity Al and shifted to 630°C for Al-Cr alloys. Amount of hydrogen trapped by dislocations increases in the alloys depending on Cr content. Microstructural hydrogen trapping behaviour in low-and intermediate temperature regions observed here was in coincidence with previous data obtained for RS materials using thermal desorption spectroscopy (TDS). The present results on hydrogen thermal desorption evolution indicate that the effect of oxide surface layers becomes remarkable in TDA measurements and show advantages in combinations of both desorption analysis methods to investigate hydrogen desorption kinetics in materials.

Effect of Rapid Solidification on Microstructural Features of Al-Cr Alloys

Microstructure of rapidly solidified (RS) pure Al and Al-0.8; 1.0 Cr alloys (at %) foils was examined with reference to near surface composition, solute/microstructure interactions, and surface topography. The hydrogen desorption from Al-Cr alloys was investigated in order to clarify effect of rapid solidification processing (RSP) on hydrogen trapping in specimens. It is suggested that hydrogen occupancy for vacancy traps in the alloys is decreased in contrast to that reported for pure Al foils and is related to the formation of vacancy-alloying element atom complexes.

Effect of Small Additions of Fe on the Tensile Properties and Electrical Conductivity of Aluminium Wires

Although low-alloyed aluminum has been used as electric line and cable materials to date, there still is a great demand for higher strength with retaining the good electrical conductivity and ductility. In the study, iron has been chosen as an additive element and the addition effect on the strength and electrical has been investigated since iron is reported to have a marked solution-strengthening effect at a given addition amount. Aluminum with 99.99mass% purity and Al-Fe alloys with iron up to 0.9mass% were induction-melted, continuously cast into a rod with 8mm diameter, and cold-drawn into a wire with 0.3mm diameter. Tensile test and electrical resistivity measurement were carried out on the rod and wire after each pass. It was found that, in the rod, the strength increased while the ductility and electrical conductivity decreased as the addition iron amount was increased. Work hardening occurred clearly at an early stage of cold drawing, while it became sluggish as the cold reduction increased in each material. At the early stage, the strengths increased as the iron amount was increased, and at the later stage, the alloy with iron addition of 0.9mass% had higher strengths and larger elongation to failure.

High Temperature Deformation Behavior of a Beta Titanium Alloy for Biomedical Application

The deformation characteristics of a beta-type Ti-29%Nb-13%Ta-5%Zr alloy, developed for biomedical application, and their relation with the microstructure are investigated. The cold-rolled specimen is subjected to a tensile test at high temperatures ranging from 700 to 800°C under a constant cross-head speed ranging from 1×10-4 to 1×10-2s-1. The elongations tested at different temperatures are compared with that of Ti-15%V-3%Cr-3%Sn-3%Al, a typical beta titanium alloy. The deformation mechanism is characterized from the parameter of the strain rate sensitivity. The microstructures before and after the tensile test are observed with optical microscope and the correspondent grain sizes are measured. The grain growth during the deformation is also described.

Influence of Stress State on Superplastic Deformation Behavior in a Zn-Al Eutectoid Alloy

A Zn-Al eutectoid alloy known as a fine-grained superplastic material is tested both in tension and compression under superplastic conditions, and the influence of the stress state on superplastic deformation behavior, such as flow stress, is investigated. In the compression test, deformation is interrupted and turning is performed to remove a barreled portion so that the gauge section becomes uniform, and then the deformation is continued. Microstructural change during the deformation is also investigated. As a result, flow stress in the compression becomes higher than that in tension even after the barreled portion is removed. After deformation, grain growth is observed both in the tension and compression, and growth rate in the compression is larger than in the tension.

Superplastic Behaviour and Microstructure Evolution in a Commercial Ultra-Fine Grained Al-Mg-Sc Alloy

An Al-6%Mg -0.3%Sc-0.3%Mn alloy was subjected to equal-channel angular extrusion (ECAE) at 325 o C to a total strain of about 16 that resulted in an average grain size of about 1 μm. Superplastic properties and microstructural evolution of the alloy were studied in tension at strain rates ranging from 1.4x10 -5 to 1.4 s -1 in the temperature interval from 250 to 500 o C. It was shown that this alloy exhibits superior superplastic properties in the wide temperature range 250-500°C at strain rates over 10 -2 s -1 . The highest elongation to failure of 2000% is attained at a temperature of 450 o C and an initial strain rate of 5.6x10 -2 s -1 with the corresponding strain rate sensitivity coefficient of about 0.4. Two different fracture mechanisms were revealed in high strain rate superplasticity. At temperatures higher than 300 o C and/or strain rates less than 10 -1 s -1 , failure took place in brittle manner practically without necking and cavitation played a major role in the failure. In contrast, at low temperatures and/or high strain rates, fracture occurred in a ductile manner suggesting the fracture of samples by localized necking. At these conditions, evidence of very limited cavitation was found in the samples.

Achievement of Low Temperature Superplasticity in a Commercial Aluminium Alloy Processed by Equal-Channel Angular Extrusion

A commercial Al-4.1%Mg-2.0%Li-0.16%Sc-0.07%Zr alloy was used as a starting material. The submicrocrystalline structure with an average grain size of about 0.8 μm was developed by equal-channel angular extrusion. Superplastic behavior of this alloy was examined in the temperature range 150-250 o C at strain rates ranging from 1.4x10 -5 to 5.6x10 -2 s -1 . A maximum elongation-to-failure of 440% was recorded at 175 o C (0.5Tm, where Tm is the melting point) and a strain rate of 2.8x10 -5 s -1 . The strain rate sensitivity was measured as 0.32 at these conditions. This temperature is exceptionally low for superplasticity in Al-based alloys, as it has been reported to date. Features of superplastic deformation at such the low temperature are considered.