Showing papers in "Journal of Japan Institute of Light Metals in 2003"

Al–Mg–Si合金の全伸びと破断形態に対する銅，銀および金添加の影響

Abstract: The effect of the addition of copper, silver and gold on age-hardening, total elongation and fracture morphology of Al–Mg–Si alloys was investigated by hardness measurement, tensile test, observation of fracture surface by scanning electron microscopy, and transmission electron microscopy. The addition of copper for the base and excess Si alloys increased the peak hardness of alloys, while the addition of silver or gold did not show any modification of peak hardness. The total elongation of alloys bearing copper, silver or gold was improved, when the tensile test was performed for peak aged alloys. Fracture surfaces of alloys bearing copper, silve or gold included the region of transgranular fracture, while those of alloys without additional elements were mainly intergranular fracture. Surface relief and fine slip bands were observed on fractured samples of alloys bearing additional elements. Mean width of precipitate free zones (PFZ) in alloys bearing additional elements was narrower than that without additional elements. According to results of this work, it is considered that additional elements of Cu, Ag and Au improve total elongation of peak-aged Al–Mg–Si alloy because prior deformation around grain boundaries during tensile deformation was controlled by the formation of narrower PFZ than alloys without these elements.

Al–Mg–Si系合金板材の機械的性質に及ぼす鉄量の影響

Abstract: The influence of iron content on mechanical properties of Al–1.0mass%Si–0.5mass%Mg–0.1mass%Mn alloy T4 sheets was investigated. The amount of Al–Fe–Si second phase particles increased with iron content, thus silicon atoms were consumed by formation of Al–Fe–Si particles. Furthermore, tensile strength of the samples in T4 condition was not influenced by iron content, but the paint bake response decreased over 0.5 mass%. This was the result of lowering age hardening rate at the early stage of artificial aging because of the loss of silicon atoms. Also, bendability of the samples became worse with iron content. But, it was the worst at 0.5 mass% of iron content, while it at over 0.5 mass% became better or the same. The reason was considered as below. Cracking by bending occurred along the second phase particles and the shear bands. And the amount of second phase particles increased with iron content, whereas the formation of shear bands decreased with iron content over 0.5 mass% because of the loss of silicon. In addition, formability became worse slightly with iron content.

Al–Mg–Si系合金の曲げ加工性に及ぼすミクロ組織の影響

Abstract: 近年,地球環境問題がクローズアップされ,世界規模で 様々な環境改善が展開されてきた。その一つとして地球温暖 化をもたらすCO2ガスの排出量を規制する動きがあり,自 動車メーカ各社は自動車の燃費低減に効果的な車体軽量化 に積極的に取り組んでいる。そして,軽量なアルミニウム ボディシート材がフード,フェンダ,トランクリッドなど の部品に多く使われるようになった。その中で,Al-Mg-Si 系合金板はプレス成形時にリューダース模様が出ないこと と塗装焼付時にベークハード性を有することなどからアウ タパネルに採用されるケースが多くなってきた。アウタパ ネルとインナパネルを一体化させるために,アウタパネル にヘム曲げ加工を施す必要があるが,Al-Mg-Si系合金は Al-Mg系合金に比べてヘム曲げ性が劣るため,その改善が 強く望まれている。これまで,佐賀らは結晶粒界上にMg2Si やSi相の析出物が数多く存在すると,曲げ特性が劣化する ことを報告した1),2)。また,過剰Si量が多いほど,合金の 耐力が高いほど曲げ特性が低下すると報告されている3),4)。 最近,浅野らは曲げ特性に及ぼすせん断帯と第2相粒子の影響 を報告した5)。しかし,曲げ割れの初期状態を観察した報告例 が少ないため,粒界割れ,粒内割れ,割れの起点と割れの伝播 などに関して依然として不明な点が多い。また,第2相粒子の 種類,サイズ,密度の影響について必ずしも明確になったとは 言えない。 そこで,本研究では,Al-Mg-Si系合金で固溶度の違うSiと Fe元素の添加量を変化させて第2相粒子の分散状態並びに添 加元素の固溶状態の相違が曲げ割れ形態に及ぼす影響を調査 し,そのメカニズムの解明を試みた。 2. 供試材の化学成分と実験方法

Mg–Al–Zn系合金の押出性に及ぼす亜鉛およびマンガンの影響

Abstract: The effects of zinc and manganese content on extrudability of Mg–Al–Zn system alloys have investigated. Zinc enhanced occurrence of surface cracks. Hence,as the zinc content increased, the extrusion speed limit became low. When the manganese and zinc content was high, the surface oxide film was thick and the surface color of the extrusion was black. On the other hand, manganese had the effect of increasing the tensile strength, 0.2% proof stress and elongation. Manganese enhanced the dynamic recrystalization in the extrusion process. As the result, the grain size of the extrusion was small.

Changes in formability at room temperature with rolling conditions of AZ31 magnesium alloy sheets

Abstract: It is well known that sheet forming of magnesium alloys is inferior in comparison with other metal sheets. In this research, in order to examine bending, stretching, formability and drawability of AZ31 magnesium alloy sheets, the effects of rolling conditions of the sheet were investigated by the model experiments. The hot rolled sheet with reduction of 1 pass 30~50% at the high temperature showed good value. Furthermore, various properties were improved by final annealing temperature of the alloy sheet. In the bending test, the ratio of radius (R) to thickness (t) for the rolled sheet showed the value of 2 in final annealed temperature at 573–673K. In the stretching test, the best biaxial deformation limit was obtained in the 50% hot rolled sheet after annealed at 623 K. In the drawing test, the sheet of LDR showed the value of 1.7 in the 30% and 50% hot rolled sheets after annealed at 573 K. These results implied that good formability of AZ31 magnesium alloy sheet was obtained by selecting proper rolling conditions.

Al–Mg–Si系合金板材の粒界腐食およびSCC特性

Abstract: Properties on intergranular corrosion (IC) and stress corrosion cracking (SCC) of three Al–Mg–Si alloys with a fixed Mg content were studied. IC test samples and tensile specimens were prepared from cold rolled sheets of alloy No. 2 (Al–0.7%Mg–0.45%Si), alloy No. 5 (Al–0.7%Mg–1.1%Si) and alloy No. 7 (Al–0.7%Mg–0.45%Si–0.34%Cu), subjected to solution treatment and then aging at 448 K. When immersed in an acid NaCl aqueous solution based on ISO11846–B method, alloys No. 2 and No. 5 were immune to IC, while alloy No. 7 showed a high sensitivity to IC under a wide range from underaging to overaging. Tensile tests by SSRT (slow strain rate technique) in the solution of IC tests were carried out to evaluate the index I of susceptibility to embrittlement as the ratio of reduction in elongation, compared to that in laboratory air. The index I of peak-aged specimens was ranked on the order of alloy No. 5 > No. 2 > No. 7, which disagreed with the tendency of IC susceptibility. Intergranular stresscorrosion cracks occurred in the SSRT tests were attributed to strain-induced APC (active path corrosion) for alloys No. 5 and No. 2, accompanied with preferential breakdown of surface film along grain boundary zones, while for alloy No. 7 to pre-existing APC caused by solute-depleted zone along grain boundaries.

Grain refinement and stretch forming of AZ31 magnesium alloy sheets

Abstract: The grain refinement of AZ31 magnesium alloy sheet was attempted by giving various plastic deformation to improve press formability. As a result, no grain refinement was attained in uniaxial and biaxial tension deformation, but the remarkable refinement was achieved in shear and compression. The effect of the grain refinement on the bulging formability was examined. Although the forged sheet with fine grain could not be bulged at temperatures between room temperature and 150°C, it could be bulged at above 200°C. Compared to the as-rolled sheet with coarse grains, the forged sheet could be formed at 100°C lower temperature to get the same bulge height.

Effects of grain size on deep drawability of AZ31 magnesium alloy sheets into square cup.

Abstract: The influence of grain structure on the formability of an AZ31 magnesium alloy rolled sheet was examined by deep drawing for five materials. Each sheet was formed at a drawing speed of 60 mm/min into a cup, which had a square bottom of 50 × 50 mm2, and a maximum depth of 18 mm. It was found that the materials with grain sizes of ≤10 μm could be formed to the maximum depth without cracking, even at the lowest temperature investigated (423 K). Tensile mechanical testing of the rolled sheets revealed that these materials with high drawability also had a high Lankford value at the forming temperature. In addition, the surface roughness at the corners of the deep drawn cup was somewhat reduced in the fine–grained materials. The present results suggest that a magnesium alloy sheet with a fine–grain structure has the potential for deep drawing at relatively low temperatures.

Behavior of Hydrogen in Al-Mg Alloys Investigated by Means of Hydrogen Microprint Technique

Abstract: In recent years, hydrogen has been attracting attention as a clean energy. For its transport, a tank for liquid hydrogen is necessary, and 5083 aluminum alloy has been chosen as a candidate of the tank material. On the other hand, hydrogen is thought to permeate most metallic materials from a corrosive environment, resulting in hydrogen embrittlement. In the actual liquid hydrogen tank, only one side of the inner sheet material is exposed to hydrogen gas. Although serious environmental embrittlement of aluminum alloys by molecular hydrogen has not been reported so far, the behavior of hydrogen has not been investigated in detail in this condition.In the present study, analysis on the permeation and migration behavior of hydrogen atoms in the above condition has been made by means of hydrogen microprint technique on a sheet of 5083 aluminum alloy, together with Al–4.5mass%Mg binary alloy which is a base material of the 5083 alloy. It was revealed that hydrogen atoms can invade and permeate aluminum alloys from the gaseous hydrogen atmosphere. The entrance site was thought to be the second phase particle and the fresh surface produced by the plastic deformation. Once hydrogen atoms entered the alloys, they were deduced to act in the same manner as impurity hydrogen atoms: migrate with gliding dislocations or by a short-circuit diffusion along dislocation lines, be transferred to grain boundaries or interphase boundaries and finally be evolved at slip lines, grain boundaries, and second phase particles on the surface.

Effect of surface roughness on glossiness of a 5052 aluminum alloy

Abstract: In this paper, the eŠects of topography with diŠerent rough surfaces on glossiness are investigated experimentally in order to characterize a surface texture of an aluminum alloy A5052H34. The surface texture of aluminum alloy is determined by the glossiness and the three factors of surface roughness: arithmetical mean Ra, period of roughness proˆle and slopes of the roughness. The surface of sample used in the experiment has diŠerent rough surfaces due to diŠerent cutting process. The topography of sample was measured by using a mechanical stylus proˆlometry. The periodic of roughness was evaluated by mean width of the proˆle elements RSm. The experimental results showed that the glossiness slightly increased as Ra decreased. As glossiness increased, RSm decreased. These means that the surface with low amplitudes and short wavelengths of the roughness results in high glossiness values. Moreover, histogram of the re‰ection angle calculated roughness proˆle showed that the specular re‰ection values of glossiness decreased as the diŠuse re‰ection values increased. Thus the local slopes of the roughness correlate strongly with the glossiness. These results clearly veriˆed that the proposed method for evaluating the surface texture of aluminum alloy was eŠective. (Received October 2, 2002)

Creation of aluminum alloy by severe plastic deformation of cutting chip and its mechanical properties

Abstract: Cutting chip is, generally, separated from cutting oil and then remelted for recycling solely as raw materials. In terms of microstructures, however, the cutting chip may be identified utilizable due to highly-accumulated strain during its formation. In this study, aluminum chips are consolidated by cold severe plastic deformation so that their highly deformed microstructure is utilized for the strengthening of an aluminum alloy. After a preliminary investigation in which a variety of cutting processes and conditions are examined to find the optimum one for the present purpose, the aluminum chips have been successfully consolidated by a combination of pressing and swaging. The consolidated chips exhibit superior strength together with finer microstructure to a wrought alloy when compared at a same applied strain. In addition, a couple of methods are demonstrated effective to eliminate the undesirable effects of oxide film on the surface of the chips, which inevitably causes debonding during loading.

Effects of tool radius on formability during deep drawing of AZ31 magnesium alloy sheets

Abstract: In previous studies, it is known that forming products with practical depth made of AZ31 magnesium alloy sheets can be obtained by applying the warm-deep drawing, where a heated die, blank holder and water-cooled punch are used. However, influence of tool radius, which is one of significant factors on deep drawing formability, has not been examined systematically under the practical forming speed condition in which hydraulic or mechanical press machine forming are assumed. In this study, we systematically examined effects of tool radius and forming speed on the forming limit of warm-deep drawing for the cylinder and square cups. Furthermore, we studied the possibility of the reform of a square cup with small shoulder and corner radii by sizing, as it is difficult to form by only deep drawing.

Mechanical and corrosion properties of 6061 aluminum alloys recycled by hot-extrusion of cutting chips

Abstract: From cutting chips of 6061 aluminum alloy, recycled materials' plates were fabricated by extrusion and rolling. Three kinds of cutting chips, which were dry-cutting chips without cutting oil, wet-cutting chips with cutting oil and clean chips obtained by washing of the wet-cutting chips, were used for the recycling process. Moreover, non-recycled materials' plates which processed by the same extrusion and rolling using virgin materials of the same alloy as the case of the recycled materials were prepared for comparison. These four kinds of plates were characterized by carrying out ultimate analysis by fluorescent X-ray spectrometer and infrared absorption spectrometer, optical microscopic and SEM observation, tensile test, and corrosion test. Consequently, a significant difference in structures, tensile properties, and corrosion resistance was not recognized among three kinds of recycled materials, it became clear that cutting oil and detergent hardly influence the characteristics. Moreover, it was found that recycled materials had smaller crystal grain than that of non-recycled materials, and excelled in both strength and corrosion resistance. The conclusion that recycling of the cutting chips by extrusion and rolling was very promising in 6061 aluminum alloys was obtained.

Microstructure and mechanical properties of friction-stir-welded 6061 aluminum alloy sheets

Abstract: The 6061-0 aluminum alloy sheet with two millimeter thick was welded by friction-stir-welding (FSW) at various welding conditions. Microstructure of the welds was investigated by optical microscopy in order to characterize the plastic flow pattern in the weld and change in size and morphology of the matrix grain structure from the original pancake-like structure in the parent sheet. The transverse cross section in the weld revealed that the boundary between the stir zone and the TMAZ (thermo-mechanically-affected-zone) exhibited a linear shape from the top to the bottom through the sheet thickness. An onion-ring pattern, which was common in the friction-stir-welded thick plate, was not detectable in the present stir zone. The wavy striations were observed in the transverse- and longitudinal-cross section of the weld. These were traces of the oxide films on the butt surface of the parent sheet and these provided the base for the evaluation of characteristic plastic flow in the friction-stir welded thin sheet. Yield strength and UTS of the weld were almost equivalent to those of the parent sheet. On the other hand, the reduced elongation was obtained. The weld was shown to break in the HAZ (heat-affected-zone).

Ductility of 6XXX aluminum alloys at high temperature.

Abstract: Al–Mg–Si alloys have recently been used for both automotive body sheet panel in order for weight saving. However, this is partially caused by poor press formability in these alloys, though both specific stiffness and strength are sufficiently high. In this paper, the high temperature characteristics of two kinds of 6XXX aluminum alloy rolled sheets in T4 condition have been investigated with special reference to the applicability to superplastic forming. Constant cross head speed tensile tests were conducted at temperature and initial strain rate ranging from 623 K to 803 K and from 1×10−5s−1 to 1×10−1s−1, respectively. The total elongation vs. strain rate diagram has a minimum of 150% near the strain rate 1×10−3s−1 both at 773 K and at 803 K. It is to be noted that the dominant deformation mechanism changes from grain boundary sliding in lower strain rate range to transgranular deformation in higher strain rate range. Total elongation increases rapidly with decrease in strain rate resulting in superplastic elongation more than 300%. The deformation mechanism is discussed on the basis of rate controlling processes. The anisotropy in ductility is also examined.

Effects of upset timing on heat input and joint strength in friction welding of a 6061 aluminum alloy

Abstract: In this paper, the effect of the upset timing on joint strength of the friction welded joints of 6061 aluminum alloy was discussed by using the evaluation factors of the deformation heat input in the upset stage and the upset burn-off length. The results showed the followings. When the upset pressure was applied before the braking, the deformation heat input in the upset stage and the upset burn-off length were so large more that sound weld joints could be obtained easily, than that of the synchronized timing at the same welding parameters. In the synchronized timing, when the upset pressure was large, the actual pressure could not attain to a set up pressure. Meanwhile, when the upset pressure was applied after the braking, the deformation heat input in the upset stage and upset burn-off length were so small that sound weld joints could not obtained. Therefore, it was made clear by using effect of the upset timing in joint performance was much related with the deformation heat input and upset burn-off length. And the sound welded joints were obtained with 200 J/s or more deformation heat input and 2.5 mm or more upset burn-off length.

Al–Mg–Si合金の引張変形および破断挙動に対するCu添加の影響

Abstract: Al–Mg–Si alloys containing Cu and excess Si were investigated by tensile test, scanning electron, scanning tunneling and transmission electron microscope observation in order to clarify the difference of their deformation behavior. Strengths and elongations of Cu-bearing alloys were higher than those of Cu-free alloys. Cu-free alloys showed the intergranular fracture, while Cu-bearing alloys showed the transgranular fracture. Frequency of the cracking on a surface of a Cu-free alloy was higher from an early stage of deformation than that of the Cu-bearing alloy. The addition of Cu suppressed the cracking in Al–Mg–Si alloys. Folds and sharp steps of grain boundaries were observed on the surface of Cu-free alloys, while Cu-bearing alloys showed transgranular deformation with wavy slip bands. The width of precipitate free zones (PFZ) in a Cu-bearing alloy was narrower than that in a Cu-free alloy. Dislocations were observed just near grain boundaries in the fractured Cu-free alloy, while there were many dislocations in grains of Cu-bearing alloys. It was considered that the improvement of elongation in Cu-bearing Al–Mg–Si alloys was caused by the suppression of preferential deformation near grain boundaries and the decrement of cracking.

Effect of thermo-mechanical treatment on cube texture in aluminum foils for electrolytic capacitor

Abstract: The present study was carried out to clarify the effect of condition of thermo-mechanical treatment (partial annealing and additional rolling) on behavior of cube texture in high purity aluminum foils for electrolytic capacitor. Foils were partially annealed at 503, 523 and 543 K and additionally rolled to 12, 17 and 22% reduction. They were finally annealed at 573 K. All foils were evaluated by SEM-EBSP method. It was elucidated that the foil partially annealed at 523 K and additionally rolled to 17% reduction, had larger area fraction of cube-oriented grains than the other foils after final annealing. From the examination of that, it was concluded that the distribution and diameter of cube-oriented grains depended on the partial annealing temperature and that grain growth in final annealing was affected by the residual strain in grains attributed to the degree of reduction of the additional rolling. It was considered that the optimized condition of thermo-mechanical treatment enhanced growth of cube-oriented grains and suppressed the other grains. On the basis of the theory to bulge nucleation the critical diameter of growth of cube-oriented grains was estimated. The estimated diameter was compared with the distribution of the measured diameter of cube-oriented grain. The result explained well the dependence of the area fraction of cube-oriented grains on foils with different conditions of thermo-mechanical treatment after final annealing.

Localized corrosion of aluminum clad sheets in alkaline solution.

Abstract: Aluminum alloy three-layered brazing sheets, clad with sacrificial anode alloy on one side of them, have widely been used for the tube of radiators for automotive in which cooling water circulates. Inner pitting corrosion resistance of the tube has been excellent both in acidified and in neutral corrosive aqueous solutions by the effect of sacrificial anode. On the other hand, it has been reported that the sacrificial anode does not work effectively in alkaline solution, and perforation by pitting corrosion occurs in earlier testing period of time. In this report, localized corrosion characteristics in alkaline solution were investigated by immersion corrosion tests and electrochemical measurements. Based on the experimental results, new corrosion mechanism was proposed in terms of solution environment formed on cathode surface. Pitting corrosion of the core alloy grew not with the attack by the alkaline bulk solution, but with accelerated dissolution by strong alkaline solution derived from the electrochemical cell formation between sacrificial anode and cathodic core alloy. Corrosion products formed in the pit were effective for maintaining strong alkaline environment on the core alloy surface.