Abstract
The conclusion of the previous report concerning the phosphoric acid treatment was as follows:
There remains no phosphoric compound on the surface of aluminium alloy plates, if it is rinsed immediately after the phosphoric acid treatment. However, when the plates are dryed after phosphoric acid treatment, the phosphoric compound adheres strongly on the surface notwithstanding the violent rinsing operation. In this report, the positions of phosphorus deposited on the surface of aluminium alloys are revealed by the autoradiograph of P32. As a result of the experiment, the positions of P32 distribute on the surface according to the structure of the aluminium alloys.
It is not clear that whether the phosphorus deposited on the surface of aluminium alloys is a different compound or the phosphoric acid solution itself remained in small cavities. In any case the phosphorus (P32) is in the insoluble state, because the testpieces of the autoradigraph are rinsed very thoroughly.
As to Al-Mg alloy, the film of phosphoric compound seemes to grow over thesurface of the alloy. As to Al-Si alloy and Al-Si-Cu alloy, the phosphoric compound seems to deposit in the cavities of eutectic structure. As to Al-Fe series alloys, the phosphoric compound seems to deposit rather on the crystal of FeAl3 than in the cavity of crystal boundary of FeAl3. In brief, the deposition of phophoric compound by the phosphoric acid treatment does not cover all over the surface aluminium alloy but partially over it according to the microscopic structure of aluminium alloy.
