It has been difficult to determine the chill zone formed on aluminum alloy die castings by conventional or metallographic method. This paper describes a tentative method to determine it in Al-12Si-Cu alloy (JIS ADC 12) die castings.
The percentage of crystallized α-phase area rapidly increased from the surface to the depth of 0.5mm being inversely proportional to the micro-Vicker's hardness. The surface layer having micro-Vicker's hardness more than 105, corresponding the α percentage less than 60%, was defined as a chill zone.
A thinner chill zone was formed on the castings having a heavy section. The thickness of chill zone on die castings of 10mm in thickness was as little as less than 50% of that in castings of 2mm in thickness. Casting factors such as metal temperature, injection pressure, gate velocity and filling ratio in the sleeve had little effects on the formation of chill zones. Only the die temperature had an effect with a significance level of 99% on the basis of variance analysis. The thickness of chill zone had a correlation to tensile strength and elongation. An inverse correlation was found, however, when the gate velocity was changed.

View full abstract

Orthogonal cutting tests were conducted on an aluminum cast Al-Zn-Mg alloy having good machinability and little trouble in tool wear. The cutting temperature was experimentally examined with respect to the cutting speed, behavior of built-up edge, tool-chip contact length, etc.
The results obtained were summarized as follows.
In the range of cutting speed 20320m/min., the relation between cutting temperature and cutting speed was expressed by a straight line both in terms of logarithmic scale. The cutting temperature was linearly elevated with the increase of the cutting speed, but it was abruptly inflected in the midway. The coefficient of linear elevation of temperature was considerably small for the cutting speed beyond the above inflection point. The cutting temperature corresponding to the inflection point was higher with the increase in the depth of cut. The cutting speed corresponding to that point was higher with the decrease in the depth of cut, and it approximately agreed with the value at which the thickness of chips was maximum. The aspect of built-up edge in this state was varied according to the depth of cut. There would be no special correlation between the cutting speed or cutting temperature and the behavior of buit-up edge. The temperature of disappearance and the behavior of built-up edge depended upon the other cutting conditions such as the depth of cut, rake angle, etc. as well as the cutting temperature.

View full abstract

It is known that Al-Mg alloy sheets produce stretcher strain markings in stretching process. The stretcher strain markings are due to yields of two types; type-A and type-B. The type-A produces random marking and type-B produces parallel marking.
In the process of pressing, the random marking appears in the range of very slight strain and bring about a serious defect.
The authors chiefly studied the conditions for the generation of the random marking.
The results obtained were as follows:
(1) The random marking produced during stretching was observed on fine-grained (under 0.04 or 0.05 mm) and recrystallized alloy sheets; but it was scarcely observed on coarse grained (above 0.1mm) sheets.
(2) The relation between the generation of random marking and the structural change during isothermal ageing (at 200 and 175°C) was also studied. As a result, the marking was observed on all water-quenched alloy sheets. However, it was not observed on Al-8%Mg alloy sheets after the start of a subsequent age-hardening and its disappearance was continued until overageing. Whereas, the marking was always observed during 140 days of ageing on alloy sheets containing less than 6% of magnesium.
(3) The grain size at which the random marking was observed depended upon the addition of copper as a third element. The additional copper (0.10.5%) elevated the upper limit of grain size range beyond 0.040.05mm.
(4) The age-hardening of Al-8%Mg alloy sheets was accelerated by additional copper as a third element; but, the sheets of containing less than 6% of magnesium were not accelerated by copper.

View full abstract

Studies were made of the effects of kind and concentration of additives and quantity of solution per unit area upon the thickness of boehmite films formed in boiling solutions.
The following results were obtained.
(1) The thicknesses of boehmite films formed on aluminum sheets were determined in the following three kinds of solutions:
(a) In triethanolamine solution
(b) In aqueous ammonia
(c) In deionized water} treating in boiling for 60min.
As the results, the former two gave the thicknesses about twice as large as that of the last.
(2) The pH value of the above (b) solution was varied with the time of boiling. Whereas, the above (a) solution showed no such a variation. Therefore, it may be concluded that (a) solution is superior to (b) solution in the stability of pH value.
(3) A relation was found between the treating time and triethanolamine concentration for maximum thickness of boehmite film formed on aluminum sheets when the liquid quantity per unit area was 0.5l/dm². For example, the treating time was 5min. for 0.5% concentration, and was 15min, for 1.5% concentration.
(4) The thickness of boehmite film formed on aluminum sheets in 0.5% solution of triethanolamine was increased with the increase in liquid quantity per unit area; however, it was kept constant when the quantity per unit area was 3.0l/dm² or more.
It was confirmed that the following experimental equation was established between the thickness of boehmite film under the above conditions d(μ), and the treating time, t(min.): d=0.137t^2/3.
(5) The effect of the liquid quantity per unit area was found to be more marked than that of the concentration of triethanolamine on the thickness of the boehmite film.

View full abstract

The effects of the purity of water upon The formation and corrosion resistance of boehmite film were studied with electron microscope and electron microprobe analyzer.
The following results were obtained.
(1) Boehmite films formed in city water containing various kinds of impurities had smaller thickness and lower corrosion resistance and were more blackish as compared with those formed in deionized water.
(2) The composition and corrosion resistance of boehmite films formed in deionized water were nearly constant independent of the value of specific resistivity, when its value was not lower than 100, 000 Ωcm.
(3) As the results of study with electron microprobe analyzer, it was concluded that the boehmite films formed in city water containing Si and Ca elements showed blackening and the decrease in film thickness and corrosion resistance, all of which chiefly depended upon SiO₂, but scarcely upon CaCO₃.

View full abstract