Characterization of the corrosion behavior of sintered parts obtained by powder metallurgy with different manganese sulfide concentrations

Abstract

Powder metallurgy is a process widely used in automotive parts, such as gears and pistons. The presence of pores is an inherent characteristic of this process. This porosity directly affects machinability, thus making the surface finish of the material rough. One of the alternatives for improving machining is the addition of manganese sulfide (MnS) to the mix composition. This work aimed to investigate the corrosion behavior of an automotive part with a majority iron composition obtained by powder metallurgy with different concentrations of 0%, 0.5% and 1.0% MnS (mass %) and varied densities (5800 kg.m-³, 6200 kg.m-³ and 6600 kg.m-³) in immersion times of 1 h, 4 h, 8 h and 24 h in 3.5% NaCl solution (mass %). The work was undertaken by means of electrochemical tests (electrochemical impedance spectroscopy and potentiodynamic polarization) and microstructural characterization, before and after the immersion periods. The results obtained by electrochemical impedance spectroscopy revealed a drop in the corrosion resistance of the samples as the period of immersion in the electrolyte increased, where the condition without the presence of MnS showed higher corrosion resistance than the samples without MnS. The potentiodynamic polarization curves indicated a reduction in corrosion resistance with an increase in the percentage of MnS in the mixture composition.