Equation representing dependence of density on composition was deduced for dilute binary solid solutions. The constants in an expression of D/kg m⁻³=D₀+ΔD (C/mass%) were obtained from Vegard’s law. For an easy calculation from contents of commercial alloys expressed commonly in mass%, previously measured values of density were put in order, as functions of mass%. This expression was expanded to multicomponent systems and it has been clarified that the values of ΔD determined by measurement on binary alloys are also valid for Al–Zn–Mg and Al–Mg–Si–Cu systems. Using the present ΔD values, the density of rather widespread multicomponent alloys can be easily estimated, excepting Al–Si binary system which density is increased by solute Si and decreased by precipitation of elemental Si from Al(Si) solid solution. Effect of dislocations introduced by severe cold rolling is rather small. Only about 0.2% or 5 kg m⁻³ decrease of density was observed in a 87% cold rolled 6N01 alloy.

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Effect of natural aging conditions on split aging, especially bake hardenability at 170°C for 1.2 ks and 86.4 ks on Al–1%Mg₂Si, Al–1.5%Mg₂Si and Al–1%Mg₂Si–0.6%Si alloys have been studied using hardness measurement, DSC analysis and electrical resistance measurement. The increasing hardness of an Al–Mg–Si alloy with excess Si during baking at 170°C for 1.2 ks without natural aging is higher than that of Al–Mg–Si alloys without excess Si. However, the hardness of the high Si content alloy after baking at 170°C for 1.2 ks was decreasing with increasing natural aging time before baking clearly. It could be considered that the cluster which did not transfer to β″ phase formed using vacancy during natural aging on the high Si content alloy. The β″ phase of the high bake hardenability sample on DSC analysis appeared at lower temperature compared with the low bake hardenability sample. The β″ phase which was located at lower temperature on DSC analysis precipitates quickly during bake at 170°C, and the hardness was increased during baking at 170°C for 1.2 ks.

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The present authors have realized that cutting chips may be identified utilizable for the strengthening of materials due to large plastic strain accumulated during cutting. The authors have proposed up-grade recycling techniques in which severe plastic deformation in room temperature air is utilized to cutting chip mixture of dissimilar materials, thereby consolidation and further accumulation of strain are simultaneously achieved. In this study, such composite materials are produced and evaluated with combinations of 6061 aluminum/IF steel and 6061 aluminum/pure copper. It is clarified that appropriate second phase cutting chip is a BCC metal. The ultimate tensile strength of the 6061 alloy is improved approximately up to 500 MPa (about 1.6 times that of the material before cutting) when the volume fraction of the IF steel is 20%. To predict the attainable maximum tensile strength by the current method, the Eshelby equivalent inclusion model is employed. The present method is identified to have a potential of realizing 713 MPa (about 2.3 times that of the material before cutting) in the case of the 6061 alloy/20%IF steel composite by eliminating production defects adjusting the matrix/second phase combination and conditions for cutting and plastic working.

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Partial softening heat treatment of aluminum alloy sheets was investigated using heat transfer between the sheet and a couple of heated metal dies to prepare a peripherally softening blank for deep drawing. It was found, from the heat conduction analysis, that the aluminum blank could be heated to the temperature of the heated dies by contacting with them in less than 1 s and the temperature gradient more than 20 degrees/mm could be obtained near the contacting region. The temperature of the sheet contacted with the heated dies depends on heat transfer from the heated dies and the temperature recovery of their surfaces. Production of the peripherally softening blanks was examined for 5052-H24, 1100-H24 and 6061-T6 aluminum alloy sheets. In the blank of 6061 aluminum alloy sheets, the difference in hardness of the central hard part and the peripheral soft part was about 1.8 times. The softening region was changeable according to inner diameters of the heated dies.

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5052 aluminum alloy to pure titanium were friction welded using a continuous drive friction welding machine. Effect of using an insert metal on the microstructures and mechanical properties of the dissimilar friction welded joint was investigated. Friction welded joints without insert metal were observed compound layer and the thickness of intermetallic compound layer were irregular and thick. Friction welded joint with insert metal, its compound layer became thin and generated comparatively evenly. In spite of the existence in the friction welding of the use of the insert metal, the hardness of compound layer of both welded joints showed higher than those of the both base metals. Tensile strength of welded joint without insert metal showed 78% of 5052 aluminum alloy and it's fractured at weld interface. But, in case of welded joint using an insert metal, the tensile strength showed 92% of 5052 aluminum alloy. The elongation of welded joints with insert metal was improved. All the welded joints with insert metal were fractured at softened area of heat affected zone of 5052 aluminum alloy side in tensile test.

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