This paper presents the results of effects of boronizing process of AISI 321 austenitic stainless steel on its electrochemical corrosion resistance. The steel samples were boronized at a temperature of 900 • C for 6 h. In this process, a mixture powder (B4C, SiC, borax), alumina (Al2O3) and potassium fluoroborate (KBF4) was used. The evaluation of the corrosion resistance of boronized stainless steel was carried out by using the so-called progressive thinning method, consisting in determination of polarisation characteristics on increasingly-deeper situated regions of the top layer. This method made it possible to determine changes in particular corrosion parameters read out from potentiodynamic polarisation curves, thus enabling the depth profiles of these parameters. Potentiodynamic polarization tests were carried out in an 0.5 M sulphate solution acidified to pH = 2.0. It is shown that unlike unmodified steel, the boron-rich outer layer does not passivate but undergoes fast dissolution both in active-and transpassive regions in the corrosion solution.
The alloyed surface layers were produced using thin Al or AlSi20 plates, which were first diffusion bonded and then melted into the Mg substrate. The microscopic analysis showed that alloying with Al led to the formation of an Al-enriched surface layer containing a high volume fraction of an Mg 17 Al 12 phase. Applying AlSi20, on the other hand, resulted in the formation of an Al/Sienriched layer containing Mg 2 Si, Mg 2 Al 3 and Mg 17 Al 12 phases. The experimental results indicate that surface alloying of Mg with Al or AlSi20 using the presented method improved the properties of the material. The microhardness of the Al-and Al/Si-enriched layers was much higher than that of the substrate. Higher wear resistance was observed for the Al/Si-enriched layer. The alloyed layers provided a certain level of protection of Mg against corrosion. The specimens alloyed with Al showed better anticorrosive properties than those alloyed with AlSi20.
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