The use of advanced high-strength steel in the automotive industry is increasing in last decade. This is due to the restrictions to reduce fuel consumption and thereby decrease harmful carbon dioxide emissions. This paper aims to investigate welding properties of dissimilar resistance spot welded hot dip galvanized DP800–TBF1180 automotive steels using MFDC (Mid Frequency Direct Current) technology. LME crack occurrence due to the zinc coating was determined by magnetic particle test. The mechanical properties of welded joints were determined by tensile-shear, cross-tension and hardness measurements. The micro structural characterization was also performed in the weld zones of the joints. The appropriate welding parameter range were selected for welding processes by MFDC technology. Therefore, LME crack formation were not observed according to magnetic particle test. The highest strength was obtained as 17.60 kN and 5.51 kN by tensile-shear and cross tension tests, respectively with a welding current of 8 kA. In addition, a soft zone was found in the HAZ for both base metals. The hardness decrease in HAZ is more pronounced on the TBF1180 side. The soft zone hardness values of the sample S4 were approximately 330 HV, and the hardness values of the base material were measured in the range of 376-386 HV.

Evaluation of inorganic and organic compounds as corrosion inhibitors of Cu-Zn alloys in H2SO4 and HNO3 solutions was studied using potentiodynamic and impedance spectroscopy along with scanning electron microscope (SEM) and energy dispersive X-Ray analyzer (EDX) investigations. The corrosion inhibition of Cu-Zn alloys was investigated in oxy acid solutions using inorganic potassium permanganate and di-hydrogen phosphate, amino acids as environmentally safe materials, commercial cooling water, and green tea extracts. Both potassium permanganate and di-hydrogen phosphate improve the corrosion resistance of Cu-Zn alloys. Phosphate appears more effective as corrosion inhibitor for Cu-Zn alloys than permanganate. The inhibition efficiency (IE%) of the different amino acids such as valine, leucine and lysine was also calculated. The experimental results have shown that amino acid-like lysine can be used as an efficient corrosion inhibitor for the Cu-Zn alloys in oxy acid solutions. This may be due to the presence of two amino groups adsorbed together. For lysine, inhibition efficiency, IE%, of ~87 and ~59 is for H2SO4 and ~96.3 and 54.9 for HNO3 for alloy I and II respectively are observed. Due to the composition of green water have a great effect on the inhibition action on Cu-Zn alloys which reaching 91.8 and 96.5% for Alloy I and 95.4 and 87.1% for Alloy II in 0.5 M H2SO4 and HNO3 respectively. Although benzotriazole, in cooling water, is an excellent inhibitor suitable for use in a wide variety of environments, it has toxic properties. So, much of the recent researches have focused on formulating new and more environmentally acceptable preservation solutions. The green tea, as plant extract, will be very environmentally friendly. The EDX confirm the formation of a protective layer on the Cu-Zn alloys containing aluminum in Alloy II. This sequence reflects the beneficial effects of Al in Alloy II. The presence of 2.43% Al in Alloy II improves the corrosion resistance due to the formation of thin, transparent, stable and self – healing Al2O3 layer. This confirmed the results obtained from the potentiodynamic polarization measurements and EIS methods.