An aluminum alloy was joined to a silicon nitride ceramic with an Al-27.1Cu-4.7Si brazing filler metal at a brazing temperature of 813 K in a nitrogen gas atmosphere. A heat treatment at 723 K (post heat treatment at low-temperature) was performed after the joining. The joint strength was estimated from the shearing strength, and the effects of post brazing heat treatment at low-temperature and Mg content in the aluminum alloy on the joint strength were examined. Though the joint strength in the as-bonded state was very low, it increased to about 65 MPa after post brazing heat treatment at low-temperature for 7.2 ks. The post brazing heat treatment at low-temperature caused the decomposition of Al₂Cu layer at the joining interface and the Cu diffusion into the aluminum alloy. Mg addition to the aluminum alloy increased the joint strength. The effects of Mg were the dissolution of an oxide scale on the aluminum surface and the enhancement of Cu diffusion into the aluminum alloy.

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The changes of pore in DC slab, after homogenized and after rolling were systematically investigated. It was found that pore size and number in the slab after the homogenization generally increased, and over 150 μm in size of the pore near the center of slab were observed. The pore size in the center of thick plate rapidly increase after rolling, and they grow as a double in comparison with the pore size after the homogenization. In this study, to understand the change of pore size during manufacture processing of thick plate, FEM modeling of the rolling process was performed for explaining why the pore become coarse during hot rolling process. From the contrast of FEM results and measurement results of the pore, the pore coarsening phenomenon of 5052 aluminum alloy thick plate in the rolling procedure was clarified. Main conclusions are shown below. (1) The FEM results show that the pressure by the roll affects only the thick plate surface and show that there is a negative pressure (tension) taking place in the center of plate when the rolling reduction is small. Therefore, it is supposed the pore size near the center increase by the tension force. (2) It is considered that stress ratio of the thick plate (rolling direction component/directional component) can be used as one of the criteria of the porosity coarsening during rolling process.

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The effect of Al and Zn contents and annealing conditions on the microstructural evolution and tensile properties were investigated by using Mg-Al-Zn alloys containing 2.0∼4.5 mass% Al and 0.7∼1.5 mass% Zn. The number of shear bands developed during hot rolling increases with increasing Al and Zn contents. As a result, grain refinement in the as-rolled (F) specimens containing large amount of Al and Zn leads to high strength and high ductility at room temperature. At 498 K, the tensile strength of the investigated alloys is almost the same, while the elongation of the F-specimens increases with increasing Al and Zn contents, leading to 150% in Mg-4.5%Al-1.5%Zn alloy. High Al and Zn contents alloys significantly accumulate large working strain in grain interiors, and involve large amounts of high angle grain boundaries and precipitates, which can become the nucleation sites for recrystallization. Therefore, dynamic recrystallization in such alloys occurs at small strain region during tensile test. This dynamic recrystallization causes reduction of flow stress and large elongation by grain boundary sliding at high temperatures. The tensile tests at 498 K reveals that the F-specimens containing large residual working strain exhibits lower flow stress and larger elongation to failure than the specimens annealed at 623 K for 1 h as a result of occurrence of dynamic recrystallization at small strain region.

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Flow and solidification and thermal deformation coupled FEM analysis and casting experiment in the casting process of near net shaped billet semi-continuous casting were carried out in order to clarify the peculiar problems such as the surface crack and the phenomenon of the mould enclasped by shaped ingot during casting process. In this study, the flow and solidification analysis was calculated using a commercial solidification package CAPFLOW, and the thermal stress analysis was calculated by a structural analysis package ANSYS. The thermal histories from the CAPFLOW were used as input data to an elasto-plasticity model which simulated the thermal stress and deformation of the billet during the casting process. By comparing the calculated results with the experimental ones, the cause of the surface crack and the phenomenon of the mould enclasped by near net shape billet during casting process were clarified. It was proven that the surface crack of the near net shape billet originated from the force acted from the mould contacting with the billet, which is caused by the deformation of the solidification contracting. The phenomenon of the mould enclasped originated from the non-uniform deformation which arises by the non-uniform solidification in the billet cross section.

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Environmental embrittlement was studied by use of round tensile specimens of two kinds of alloys: Al-1.12 mass%Mg₂Si-0.35Si (S-alloy) and Al-1.47%Mg₂Si-0.34%Cu (BC-alloy). They were solution treated at 540°C for 1 h, quenched in water and aged at 175°C for indicated times: 30 min (under aging), 10³ min (peak aging), and 10⁴ min (over aging). After heat treating, they were tested at an initial strain rate of 1.7×10^-4/s or 1.7×10^-7/s in a laboratory air with relative humidity of about 100%. When tested at the strain rate of 1.7×10^-7/s, the peak aged S-alloy showed embrittlement with lower tensile elongation and reduction in area compared with a strain rate of 1.7×10^-4/s. The embrittlement also appeared on the other aging conditions (under aging, over aging), and it was most apparent on over-aged alloy despite their lower tensile strength. By means of EDS analysis, Si-rich precipitates were detected on intergranular fracture surface of over-aged alloy. In contrasted to foregoing experimental results on S alloy, no embrittlement appeared in the BC-alloy irrespective of aging condition. Thus, the embrittlement is thought to be stimulated by the Si-rich precipitates which are increased with the progress of aging.

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An impact test equipment was developed to measure the strength of adhesive resins subjected to impact loads at low temperatures. The stress wave propagating the adhesive layer and the adherend was analyzed by the one-dimensional elastic wave theory. It was confirmed that the average stress value in the adhesive layer could be evaluated by the stress value of the adherend. Therefore, the measurement method with this equipment is effective. The impact strength of an acrylic adhesive was evaluated using the developed test equipment. As a result of the impact test, the impact strength of the acrylic adhesive increased once with temperature decrease. However, when the temperature decreased lower than a specific value, the impact strength decreased. It was considered that this phenomenon occurs because the adhesive becomes brittle as the temperature decrease.

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The effect of welding speed on the tensile properties of the friction stir welds of Al-1.7mass%Cu-1.0mass%Mg-0.8mass%Si alloy has been investigated. The increase of welding speed improved the tensile properties of the friction stir weld after the postweld heat treatment at 468 K for 8 h. The increase in tensile strength of the friction stir welds was attributed to the reduced time above the overaging temperature in the HAZ where the tensile fractures occurred. The increase of welding speed decreased the density of the coarse precipitates with a length of 500 nm in the HAZ.

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In this study, a new method for producing aluminum-matrix composites locally reinforced with SiC particles is proposed, which applies the electromagnetic (e.m.) force to accumulate SiC particles in the periphery of an aluminum cylinder. A high frequency induction coil is used to impose the e.m. force in an aluminum melt containing SiC particles (21 μm in average diameter). The experimental conditions are as follows: weight of aluminum 0.18 kg; diameter of crucible 0.04 m; holding time of e.m. force 8-36 s; frequency 30, 80, 200 kHz; coil current 42-163 A. Particles are accumulated in the periphery of aluminum during several to several ten seconds. The particle concentration increases with increasing coil current and the thickness of the particle accumulated layer decreases with increasing frequency because of the skin effect. The particle-accumulated surface of the solidified aluminum ingot achieves a good wear resistance. The composite which is reinforced only its surface with SiC particles by this electromagnetic method, can be compressed more easily than the composite homogeneously reinforced with SiC particles.

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The development of a low-melting-point-braze based on the Al-Cu-Si ternary eutectic composition with Zn and the joining of Si₃N₄/Al alloy were investigated. The Al-27.1%Cu-4.7%Si-50%Zn alloy which has solidus point 687 K and liquidus point 699 K was made into the brazing foil using by a Rapid Quenching Device. The joining strength was obtained about 180 MPa at 773 K in the atmosphere of flowing N₂. It was considered that Zn restrained to form the Al₂Cu layer at the joining interface, because Zn made the copper solubility limit in aluminum increase and the copper diffusion into the aluminum alloy promote.

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Deep drawing is examined as an example of applying the local annealing method by the CO₂ laser. The deep drawing limit of the local annealed blank is obtained at the intersection in two kinds of breaking limit lines generated by expanding the annealed area. The limiting drawing ratio of the cylindrical shell shows D_{0 max}/d_P=2.88 (1.29 times the O blank) with D_AF/d_P=1.90. The deep drawing limit of the square shell improves by using the whole circumference annealed blank from the corner part annealed blank. The value shows D_{0 max}/s_P=2.54 (1.22 times the H26 blank) with D_AF/s_P=1.78. The drawn shell of uniform strength is obtained by using the local annealed blank that does the outer part from area (D_AF/d_P≥1.54) where the O blank is done in deep drawing and it reached the hardness of the H26 blank in annealed. Moreover, the limiting drawing ratio can be enlarged more than the O blank and the H26 blank. When strength of shell is made uniform in deep drawing of the square shell, the corner part annealed blank is effective because the work hardening of the straight side is a little.

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Vacuum die-cast and high-speed twin-roll cast products were fabricated using a heat-treatable Al-Si-Mg base alloy (A) and a non-heat-treatable Al-Mg base alloy (B). These alloys have almost equivalent tensile strength and ductility but different solidified structure. Tear toughness tests were performed using a small-size specimen and the unit crack propagation energy, UE_p, was obtained from the load-displacement curve. For the vacuum die-cast products, both A and B exhibited macroscopically plane fracture surface. Dimple formation nucleated at the globular eutectic Si particles was detected in A. In contrast to that, the fracture surface of B was covered with a lamella eutectic structure. UE_p was larger in A than B. Large increase in UE_p was obtained for the twin-roll cast products. Their UE_p values were 1.8 and 3 times larger than those of vacuum die-cast A and B, respectively. Macroscopic appearance of the twin-roll cast products was characterized by the slanted shear-type fracture path for both A and B. In addition to that, fracture surface of B showed fine dimple fracture surface. Large increase in UE_p for B is due to the morphological change of the eutectic structure from the lamellar-type to the fine and globular-type induced by the rapid cooling rate of the high-speed twin-roll casting.

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Tear toughness tests were performed for a 6 mm thick 6N01-T5 aluminum alloy plate joint by friction stir welding. Tear test specimens were collected in various ways so that the crack propagates through the selected local region of the weld, and by which, the relationship between the crack growth resistance and the local microstructure was examined. Morphology of the load-displacement curve and the obtained unit crack propagation energy (UE_p) were systematically changed reflecting the local microstructural difference in the vicinity of the weld region. As for the as-weld condition, UE_p of the weld region was larger than that of the T5 treated parent plate. For the middle of the weld region consisting of refined equiaxed grain structure (so called “stir zone”), UE_p was larger than the surrounding outer region with a pancake-like grain structure. Specimen surface observation found that fine slip lines appeared when the crack propagated through the stir zone. In contrast, a rough and coarse slip pattern was dominant when the crack propagated through the outer region of the weld zone. The obtained load-displacement curve, UE_p values and change in specimen surface appearance provided a quite reasonable correlation to the local microstructual characteristics in the weld zone.

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