The phenomena and prevention of season cracking of a new strong Al-alloy series, which were reported in the previous paper, ⁽¹⁾ have been investigated. The result obtained are summerised as follows:- Season cracking always takes place along the crystal boundaries of alloys, and hence stress alone is not the cause of it. It does not occur in vacuum, but especially does severely in such medium as saturated water vapour or sea water which tends to accelerate intercrystalline corrosion. The closer the yield point and maximum tensile strength of a certain alloy, the weaker becomes its resistance against season cracking. The length of time required to occur season cracking in an alloy varies by degree and direction of working given to that alloy. Its is thus concluded that the season cracking will not occur simply by an internal stress of a metal or a medium that surrounds the metal, but it takes place by the combined action of these two factors.
The season cracking could be greatly minimized even for these alloys susceptible to it by adding special elements to prevent intercrystalline corrosion, coating with some adequated materials, or by special working procedure.