The fatigue properties of several kinds of welded aluminum alloys for construction such as Al-Zn-Mg, Al-Mg, and Al-Mg-Si systems were investigated. The experiments were conducted on the effects of filler metals on fatigue properties of welds and the relation between tensile and fatigue strengths of the alloys.
The following results were obtained.
(1) Higher fatigue strengths were obtained when Al-Mg alloys were welded with the filler metal of Al-Mg system having the same content or higher Mg content than the parent metal.
(2) The proper filler metal for Al-1.0% Mg-0.6% Si alloy was Al-4.5-5.0% Mg alloy containing a considerable amount of Mn.
(3) Al-Zn-Mg alloys welded with the filler of the same system were higher in fatigue strength and more insensitive to notch or source of stress concentration than with the filler of Al-Mg or Al-Si system.
(4) The relation between fatigue and tensile strengths of welds was indentical with that of the parent material in the range of tensile strength up to 15kg/mm². However, when the strength was above 15kg/mm², the fatigue strength of welds showed a different behavior from that of mother plate. This would be interpreted by notch sensitivity of welded parts.

View full abstract

This report relates to corrosion-fatigue tests of 12 sorts of Al-Zn-Mg alloys in 3% aq. solution of NaCl and the effects of prior-corrosion in the atmosphere (atmospheric corrosion), in the service water (running), and in 3% aq. solution of NaCl for 2 years on fatigue strengths of 12 sorts of aluminum alloys.
The fatigue properties were examined with Ono's type rotating-beam fatigue tester, and the fatigue strengths were determined in 10⁷ cycles.
The corrosion-fatigue strengths of Al-Zn-Mg alloys were 5-6.8kg/mm², and almost no effects of heat treatment on the corrosion-fatigue strengths were observed.
The fatigue strengths of prior-corroded specimens had a tendency to decrease in the following order: atmospheric corrosion>3% aq. solution of NaCl>service water.
However, for some materials, the value in NaCl solution was higher than that of atmospheric corrosion.
Most of the reduction in fatigue strengths due to corrosion appeared during one year in the beginning. The average reduction factor of fatigue strength in atmospheric corrosion was 28%.

View full abstract

Aluminum (2S) plate is inferior to aluminum alloy plates in drilling machinability, because aluminum is a very soft material. Drilling tests were performed on aluminum plate to obtain proper drilling conditions of fishtail point drill, having a specially ground shape of tip, for good accuracy in the dimensions of drilled hole and small drilling resistance. That is, the accuracy of drilled hole was investigated with respect to diameter of hole inlet, diameter of hole outlet, heap at the hole inlet, burr at the hole outlet, etc. as well as drilling resistance by various shapes of the drill tip.
As the results, the proper drilling conditions for aluminum plate obtained in the experiments were as follows:
Chisel edge angle……about 140°
Fishtail angle……about 170°
Lip clearance angle……about 6°
Height of chisel edge……about 1mm

View full abstract

The authors have reported on structure, recrystallization, and thermal stabilization of supersaturated solid solution of Al-Mn alloys which could be obtained by quenching from molten state. In this study, the distribution of Mn and the third elements such as Cu and Zn in these supersaturated solid solutions obtained by casting in wedge-shaped copper mold held at 0°C was examined by means of electron microprobe X-ray analyzer.
The results obtained were as follows.
(1) It was found that the distribution of Mn in the wedge-shaped specimens of Al-3% Mn, Al-3% Mn-3% Cu, and Al-3% Mn-2% Zn alloys were macroscopically uniform by chemical analysis, and also, dendritic structure of these alloys, which had been crystallized at high cooling rate (higher than about 800°C/sec), was almost microscopically homogeneous by X-ray microanalysis.
(2) It was shown that the segregation of Mn to the dendrite boundaries was effectively inhibited by the addition of these third elements even in case of relatively slow cooling rate.
(3) The distribution of the third additional elements was not so uniform as that of Mn, and particularly, the segregation of Cu to the dendrite boundaries was remarkable.

View full abstract

It is well known that grain refining of aluminum alloys of solid-solution type on casting is acquired by the addition of a small amount of alloying elements such as zircon, titanium, vanadium, etc.
As the results of a few studies, some mechanisms of grain refining on casting have been proposed. One of the theories proposed was that the reason of refining is due to the combination of titanium with carbon in molten aluminum, and as TiC has a similar lattice structure to that of aluminum, it promotes the nucleation of solid aluminum in molten metal.
If TiC promotes the nucleation of solid aluminum for the reason of its lattice structure, the refining by the addition of TiN should be more effective than that by TiC, because the lattice parameter of TiN is more approximate to that of aluminum.
The authors recognized in experiments that grain size of aluminum containing titanium melted in nitrogen atmosphere was finer than that of aluminum melted with addition of carbon only.
By the application of the above result to MIG welding of aluminum, the authors compared the grain size of deposit welded in pure argon atmosphere with that welded in argon including nitroge.
The test specimens used were Al-Mg and Al-Zn-Mg alloys containing and not containing titanium or zirconium.
When aluminum alloys containing no titanium were welded, the grain size of deposited metal was not different in the case of argon and nitrogen atmosphere from the case of argon only. On the other hand, when titanium was contained in welded alloys, the grain size of deposit was very finer when nitrogen was added to argon atmosphere. The same results were also obtained in alloys containing zirconium.
Experiments were further made to determine the decrease in crack of bead by grain refining. Generally, the addition of nitrogen to argon provoked short-circuit transfer action, but about 15% of the addition did not provoke the short-circuit transfer and showed the same weldability as in the case of pure argon.

View full abstract