Factors affecting the formation of band structure and cracks, and effects of heating temperatures on the impact strength and microstructure of Al-Si-Cu alloy castings were examined. The alloys were heated at temperatures above solidus and quenched. The impact strength of the castings is found to decrease drastically compared with that of casting heated at temperatures just under the solidus. There are two reasons for the decrease, (1) band structure of quenched liquid phase with large pores is formed, and (2) many cracks are present near the surface of castings. Eutectic Si phase is on the other hand well spheroidized by heating at such a temperature range. The formation of large pores and cracks is prevented, when temperature and time of the heating were controlled appropriately and castings were cooled slowly. The band structure of quenched liquid phase is diminished by solution treatment after heating. The impact strength of Al-Si-Cu alloy castings is improved by the treatment.

View full abstract

The changes in passivation current density (I_pass) of aged Al-Zn-Mg alloys in 0.5N NaCl solution has been examined using Slow Strain Rate Technique (SSRT). The specimen was regulated within the region of passivation potential which was predetermined from the polarization curve at 298K. I_pass was fluctuated widely with increase in strain rate in the solution-treated alloy, but not in peak-aged alloy. The addition of copper decreased the fluetnation of I_pass. The fluctuation of I_pass will be caused by the dissolution and subsequent repair of surface oxide film. In addition dimple pattern which was predominantly observed in solution-treated alloy transgranular cracking probably due to the pitting corrosion was partly observed. Peak-aged alloy showed intergranular cracking caused by rupture and repair of film, together with the dimple pattern.

View full abstract

Investigations have been made on occurence of pitting of aluminum. Potentials and galvanic current between aluminum and iron in 1.0M AlCl₃ solution were measured by controlling solution resistance, which is named "iR polarization method". A pitting factor, f_pit calculated from data of iR polarization method has been examined. It is found that iR polarization method makes it easy to obtain the value of f_pit in natural corrosion state.

View full abstract

In the extraction of aluminum (III) from sodium hydroxide solutions by 7-(5, 5, 7, 7-tetramethyl-1-octen-3-yl)-8-hydroxyquinoline (Kelex 100, designated as HQ hereafter) in kerosene, the distribution equilibria and kinetics have been investigated under different conditions. From the dependence of the distribution coefficient on the concentrations of aqueous sodium hydroxide solution and Kelex 100, it is deduced that the extraction reaction can be expressed as Al (OH)₄^-(aq)+3HQ(org)_??_AlQ₃(org)+OH^-(aq)+3H₂O(aq). Besides, the kinetic results under non-equilibrium conditions suggest that aluminium (III) is taken up through either formation of two different activated species, [Al(OH)₃], OH^- or Na⁺[Al(OH)₃], OH^-, depending on the concentration of sodium hydroxide in the aqueous phase.

View full abstract

In order to know the relation between pressure and radial position as a function of stroke, billets of plasticine were extruded and extrusion pressure was measured. Using dummy blocks composed of a ring and a disk, total load and load on the disk were plotted against stroke by a XY recorder. Pressure distribution on the dummy block was obtained during extrusion by applying three sizes of the rings and disks. The pressure is higher at the outside of the billet than in the center. The pressure difference between the outside and inside increases with stroke.

View full abstract

The interdendritic fluid flow which is a potential factor controlling casting defects was studied by a simulating experiment on Na- and Sb-modified Al-7% Si alloy castings. The residual liquid in the solidifying alloys was flowed into a tube at different fractions liquid by compressing. The ratio of apparent permeability to viscosity (K/μ) of residual liquid was calculated from the flow rate of the liquid and pressure in D'Arcy's equation. The interdendritic fluid flow is flowable at fractions liquid from 0.8 to 0.3. The ratio K/μ is nearly proportional to the square of the fractions liquid and remains unchanged by Sb-modification at the same fraction liquid. The ratio is, on the other hand, decreased at the same fraction liquid by Na-modification which expands a hydrauric radius. The apparent permeability is almost proportional to the 2.5th power of hydraulic radius which depends on the geometory of dendrites. The ratio K/μ of the Na-modified alloy decreases with an increase in viscosity of the residual lquid.

View full abstract

Fourier analysis was applied to characterize solidification structures of metals. Optical micrographs of dendritic structures of some cast aluminum-copper alloys were transformed into a series of digital signals and analyzed by computer. Results of analysis were expressed as power spectrum, i.e. frequency distribution of wave length and direction. The peaks of the spectrum, i.e. length and direction of the most frequently observed wave, coincide with the spacing and direction of dendrite measured by the conventional method. Since the present method is fully automatic, it is expected to be more reproducible in characterizing solidification structures than when using the conventional concept of dendrite arm spacing, which is often dependent on personal judgement and skill. Besides the information of the major wave element, information on minor wave elements is also obtained by the present method and can be utilized if necessary.

View full abstract