The structure of melt spun Al-Fe alloys was investigated by HREM (high resolution electron microscopy), Mossbauer spectroscopy and X-ray diffraction. Rapidly quenched Al-Fe alloys consisted of the aluminum rich fcc crystalline phase dominantly and iron rich second phase composed of ultra fine scattered centers with a size of ten nanometer observed in the grain boundary region as well as in the matrix. The amount of soluted iron atoms in the fcc phase estimated from a Mossbauer spectrum increased with iron content. A good correlation was obtained between the concentration of soluted iron and the change in lattice parameter.

View full abstract

The SCC of three kinds of Al-Zn-Mg alloys in 0.6N NaCl solution was studied by the PSSRT (Potentiostatic Slow Strain Rate Technique) in connection with its polarization behavior. Specimen (A) containing Cu, specimen (B) containing Mn and specimen (C) containing Cr, Mn and Zr were used in this investigation. The potential of these specimens was regulated in the region of the pitting potential or passive potential, which was found from their polarization curves in 0.6N NaCl solution at 298K. The fracture surface of specimens was observed by Scanning Electron Microscope (SEM).
At the pitting potential region, all specimens fractured transgranularly at the surface of the specimen. For specimen (A) and (B), transgranular cracking and intergranular cracking were observed. However for specimen (C), intergranular cracking could not occur under the condition of this investigation.
At the passive potential, intergranular cracking occurred for specimen (A) and (B), but it could not occur for specimen (C) under the condition of this investigation. Transgranular cracking was considered as SCC induced by pitting corrosion, and intergranular cracking as the rupture of the brittle oxide film along grain boundaries. Therefore, intergranular cracking susceptibility was explained from the viewpoint of growth of oxide film. From all these results, the mechanism of SCC of Al-Zn-Mg alloy was illustrated schematically.

View full abstract

The flash formation times in four types of casting processed by four types of pressure die casting machines (500-1650tons) were studied by measuring the metal flow behavior in the die cavity and the plunger stopping time. The flash in the product area and near the overflow area was formed only when molten metal was filling in the cavity. The flash near the biscuit and runner area, however, occurred after the molten metal had filled in the cavity, as well as occurring while the molten metal was filling in the cavity. This result has also been demonstrated by the cross section structure of the flash.

View full abstract

Vacuum brazability of aluminum hollow receptacles has been investigated in relations to the degree of close and magnesium content in brazing sheet claddings. The degree of close was varied by changing the hole diameter in brazing sheet attached to top and bottom side of a cylindrical aluminum pipe. Outside fillet formation was only dependent on the magnesium content of brazing sheet, however, fillet at inside was dependent on both degree of close and magnesium content. At relatively completely closed circumstances, relatively large fillets were obtained irrespective to magnesium content. At open circumstance or outside, large fillets were obtained except brazing sheet with 0.5%Mg. The lowest brazability was obtained at medium degree of close. Auger electron spectroscopy on brazing sheets and aluminum pipe after brazing revealed that the existence of the surface layer with much MgO and/or thick Al₂O₃ were responsible to the poor brazability in medium degree of close.

View full abstract

Al-4.5%Cu alloy ingots were produced under different levels of such variables as keeping time under the pressure, delay time for pressurization, applied pressure, pouring temperature, mold temperature and height/diameter ratio (H/D). The macrostructure and macrosegregation were measured on the longitudinal section. Macrosegregation is almost independent of the keeping time, delay time for pressurization and applied pressure. Pouring at high temperatures, mold preheating at high temperatures and the use of a small height/diameter ratio (H/D) are preferable to moderate macrosegregation. The segregation is greatly affected by liquid feeding compensating solidification shrinkage. Channel type segregation is often produced along the path of liquid feeding.

View full abstract

The superplastic behavior of Al-4.5%Cu-0.5%Zr and Al-5.9%Cu-0.5%Zr alloys was studied. Both the alloys 20 to 30μm in grain size at initial recrystallization and 40 to 60μm after hot deformation show superplastic elongation only up to 250% at any temperatures and strain rates. Significantly fine grained structures 5μm in size are achieved after an initial straining stage only by deformation at temperatures being elevated. This microstructural change is attributed to strain-induced continuous recrystallization basing on the texture analysis. These alloys ensure superplastic elongation 1000% or more. Deformation at temperatures being elevated from 400° to 540°C at an initial strain rate 2.5×10^-3s^-1 is required for both alloys to attain a high level of superplasticity. It is also recommended to predeform at strain rates more than 20% strain and at temperatures at least 385°C and to deform successively at an initial strain rate 2.5×10^-3 s^-1 at 540°C.

View full abstract