Formation of the fir-tree structure in DC cast 5005 alloy was studied by means of Xray-diffraction and optical microscopy comparing with that of Al-Fe-Si alloy (1100). Unidirectional solidification experiments and direct measurements of cooling rate during solidification in DC casting process were also made. The main intermetallic compounds in the outer and inner regions of fir-tree structure in DC cast 1100 alloy are respectively Al₃Fe and Al₆Fe as shown in the previous works. The major phase Al_mFe is found in the outer region in 5005 alloy and Al₆Fe and Al₃Fe in the inner region. A clearly shaded boundary lies between Al_mFe and Al₆Fe (or Al₆Fe + Al₃Fe) phase regions in the ingot of each alloy unidirectionally solidified. The cooling rate at the boundary(the minimum cooling rate for Al_mFe formation, Vc) in 5005 alloy is smaller than those in Al-0.5%Fe and 1100 alloys, and is in the range of cooling rate in DC castings. The fir-tree structure of Al_mFe is formed when cooling rate near the surface of DC cast 5005 alloy exceeds Vc.

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Hardness measurement, X-ray small angle scattering diffraction and transmission electron microscopy were carried out on the Al-4.5%Zn-1.2%Mg alloy welds. Dissolution, reversion, and partial reversion or coarsening of precipitates occur during welding in the heat-affected zones of the T4 and T6 treated materials. These structural changes depend on the peak temperature during welding or the distance from weld center. Softened zones are formed during post-weld aging at room temperature in the heat-affected region where partial reversion take place during welding. Softening in the heat-affected zones of these materials is attributed to differences in vacancy concentration, size distribution of precipitates and coarsening of precipitates.

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Al-2.7wt%Fe and Al-3.25wt%Fe alloys were unidirectionally solidifed where the temperature gradient G and solidification rate R were controlled and uncotrolled, respectively. The Al-2.7wt%Fe alloy has three types of structures i. e. platelet eutectic, mixture of platelet and fibrous eutectics and flaky eutectic having primary α corresponding to G and R. The interphase spacing λ of FeAl₃ is: Rλ² = 5.8 × 10^-3 (cm³/sec). The structure of the Al-3.25wt%Fe alloy changes from Al-FeAl₆ eutectic cells including primary FeAl₃ with α hallo to those including Al-FeAl₃ eutectic and finally to Al-FeAl₃ eutectic with primary FeAl₃, corresponding to decrease in G, R and G/R. The spacing λ of regular rod-type FeAl₆ is expressed as Rλ² = 2.5 × 10^-10 (cm³/sec). Transition from Al-FeAl₃ to Al-FeAl₆ eutectic occurs within a range of R from 2.6×10^-2 to 4.6×10^-2cm/sec (G less than 9°C/cm). The Al-FeAl₃ alloy solidified at R from 1 × 10^-3 to 2×10^-3cm/sec has maximum tensile strength. The micro-hardness of the Al-FeAl₆ eutectic increases with decrease in λ.

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Fractography was made on tension tested specimens of the Al-Si alloys (2-20%Si) solidified under the hydrostatic pressure up to 3000kgf/cm². A slant fracture is found in the hypoeutectic alloys solidified under the pressure, and a fibrous fracture in the eutectic alloys solidified under the pressure. The hypereutectic alloys and all the alloys solidified under 1 atm show cleavage fractures. Topographies of the fractures both of the hypereutectic and eutectic alloys are nearly flat. Dimples are found in the hypereutectic alloys solidified under the pressure above 1000kgf/cm². Large dimples are formed around the inclusions, and small ones between the large dimples.

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This work intends to ascertain whether surface defects in indirect extrusions can be prevented or not only by means of usual and available extruding conditions, namely the clearance between container wall and die, arrangement of holes in a die, temperature etc. 4043 alloy wire was tightly wound on the circumferential surface of 6063 billet to simulate the metal flow of billet surface. The test result was reaffirmed in practical operations. Great difficulties are encountered in preventing the surface defect in indirect extrusions of 6063 DC billet.

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Brushing, dipping in caustic soda, peeling, grinding and lathe scalping were tried in place of inefficient removal of container skull to finish the billet surface which often causes surface defects in indirect extrusions. They are inapplicable because of poor reliability, difficulty in equipment, low recovery and poor economy. An economical and reliable "billet profiling-scalping machine" has been developed in which a profilling mechanism is equiped in a lathe. The machine ensures improvement in scalping recovery, automatic operation and preventing surface defects in 6063 extrusions.

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