Abstract
In order to inprove the corrosion resistance to chloride-containing aqueous solution of steel for concrete reinforcement, an attempt were made to form a low Al alloyed layer on steel surface by the powder packing method using a mixture of Al2O3 and Mg powders. The surface Al concentration and the thickness of alloyed layer increased with the increase of the treating temperature and time and Mg content in the powder mixture. In the case of the powder mixture containing SiO2, the surface Al concentration and the thickness of the alloyed layer decreased with the increase of SiO2 content. On the other hand, the surface Si concentration increased with SiO2 content up to 5 mass%SiO2 and then decreased. The anodic polarization tests showed a corrosion potential of −430 mV, a current density for maintaining the passive state of approximately 7 μA·cm−2, and a pitting potential of +600 mV for the specimen having the surface composition of about 10 mass%Al. The corrosion potential increased and the pitting potential declined when the surface Al concentration was increased or decreased. In the case of a low Al-Si alloyed layer containing 4.8 mass%Al and 1.8 mass%Si, the pitting potential was almost the same as that of the low-Al alloyed layer, but the current density for maintaining the passive state was remarkably lower. In tensile and bending tests, it was found that an alloyed layer having the surface composition of about 10 mass%Al did not degrade the mechanical properties of the parent material and that it had excellent adhesion with the parent material. An alloyed layer could be formed even by heating specimen in no contact with the powder mixture. From this fact, it is concluded that Al2O and SiO vapors produced in the powder mixture is reduced by Mg vapor on the surface of the specimen, forming the alloyed layer.
