In order to investigate the influence of second-phase particles on chip breakability of aluminum alloys, turning test for various wrought aluminum alloys were carried out with carbide inserts (K10) in dry and wet cutting conditions. In the materials, Al₂Cu, Mg₂Si, Al–Fe–Si system compound and eutectic Si were observed as second-phase particles. Chip breakability of materials which containing Al₂Cu or Si as second-phase particles were superior than that of materials with Mg₂Si or Al–Fe–Si system compound. This tendency was more prominent in wet cutting than in dry cutting. The Al₂Cu and Si particles on the machined surface were fractured by cutting tool in machining. It was estimated that those fractured second-phase particles acted as nucleus of chip breaking during machining. Moreover, the increase of the chip breakability in wet cutting was attributable to the promotion of fracture of Al₂Cu and Si particles due to the Rehbinder effect.

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Formability of extruded round AZ31 magnesium alloy pipes with different manganese concentrations was evaluated by performing bending tests and measuring strain along the length of the pipes during the bending process. It was found that an increase in the amount of manganese content from 0.3% to 0.7% did not exert any significant effect on the values of yield stress, elongation, or compression to fracture, while the values of hardness tended to increase and UTS decreased. The compression ductility was significantly lower than tensile ductility for all manganese concentrations. Accordingly, the formability of pipes decreased, causing cracks in areas where compression strain occurred during bending. It was also found that a larger strain occurred in the latter half of the region along the length of pipe between the clamp-end and pipe positioning block. For alloy pipes with higher manganese concentrations (0.5 and 0.7 Mn mass%), there was a clear strain peak occurring in the strain profile in the region, while for the 0.3 Mn mass% alloy pipe it exhibited a more uniform strain profile along the length of the pipe in this region, indicating that a more uniform deformation took place which was confirmed by microstructure analysis of the specimens.

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It is generally believed that formability of magnesium at room temperature is poor, owing to its crystal structure, hcp. However, in the case of high purity magnesium, cold-rolling at room temperature is easily carried out with higher rolling reductions. In the present study, high purity magnesium specimens with about 1 mm in thickness were prepared by a vapor deposition technique, which intrinsically possesses a purification process during evaporation and deposition. Cold-rolling with about 80% reduction can be applied to the specimen by a multi pass rolling without any cracking, except a small ear cracks. Moreover, it has been found out that recrystallization was induced by cold-rolling when the reduction rate was larger than about 30%. The (0001) texture was formed by cold-rolling, which did not deteriorate the formability. Non-basal dislocations were frequently observed in the cold-rolled specimens. Critical resolved shear stress for the non basal slip system is considerably lower in the high purity magnesium compared with those in the conventional magnesium and its alloys, which results in cross slip and annihilation of dislocations and causes the recrystallization.

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Low temperature superplasticity was studied in a fine-grained magnesium alloy AZ31 which was processed by multi-directional forging (MDF) under decreasing temperature conditions. Tensile specimens were machined from MDFed Mg alloy parallel to the final compression axis. Tensile tests were carried out at temperatures from 393 K to 473 K and at various strain rates. Superplasticity appears even at 393 K with a stress exponent of around 5.6 and a total elongation of 370%. The relative large stress exponent can be connected with grain coarsening or refinement taking place during deformation. The initial texture introduced by MDF hardly changes during deformation. These suggest that grain boundary sliding can take place during superplasticity, while grain rotation hardly occurs.

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For 6061-T6 and 7075-T6 aluminum alloys as candidate liner materials for high-pressure hydrogen container, SSRT (slow strain-rate technique) tests in humid air with 90% relative humidity were carried out to evaluate the susceptibility to hydrogen embrittlement (HE) and to reveal the process of HEAC (hydrogen-environment -assisted cracking). 7075-T6 showed a significant susceptibility to HE, resulting in intergranular cracking, while in contrast, 6061-T6 exhibited an excellent resistance required as liner materials. HEAC of 7075-T6 is confirmed to progress as follows; at the first stage micro-cracks originate at inclusions of Al–Fe–(Cu) phase on the specimen surface and then advance to intergranular cracking. 6061-T6 would not give rise to micro-cracks because of less localization of slip deformation enhanced by hydrogen effects, mainly due to the precipitation microstructure.

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