It is well known that the internal stress in aluminium alloys is due to cold working. From the inference that the weakening of grain boundaries of the alloy in which remains the internal stress, causes cracking just in the same way as the season-cracking of copper-alloy, the author performed this research.
In detecting grain boundaries of aluminium-alloys, the salts of mercury seem suitable and as mercurous nitrates do not act to aluminium-alloy, a saturated solution of mercuric chloride was tested. But by another experiment it is found that the addition of 1/15 N HO to that solution gives still more satisfactory result. By this solution, some of the cold drawn duralumin, super duralumin and aluminium-alloy containing Zn 8%, Mg 1.5% and Cu 2% cracked in a few seconds.
The internal stress in these alloys caused by a working ratio was studied and it was found that a stress of 10kg/mm2 or more in hollow sunk duralumin tubes could be easily detected by this solution. By annealing the duralumin tubes having 20kg/mm2 stress at various temperatures and durations, it was found that at an annealing temperature of 275_??_300° the solution indicated the removal of stress to a great extent. Drawn super duralumin and aluminium-alloy bar containing Zn did not also show cracks by annealing at 275° and 250° respectively. According to Rosenhain the season crack in an E-alloy containing Zn could be prevented by adding 0.5% of Mn to it. In order to prevent the season crack of an alloy containing Zn 8%, Mg 1.5% and Cu 2% the author added to it a small quantity of Mn, Mo and Cr, but made little s_??_ccess.
Please do not copy without permission.