Development of Zn50 Brazing Alloy for Joining Mild Steel to Mild Steel (SAE1018)

Abstract

This work has developed new brazing alloys for joining mild steel to mild steel (SAE1018) at a lower temperature. The alloys blends and error analysis were done by experimental design software (Design Expert 8.0.7.1). Design of experiments was done by Scheffe quadratic mixture method. The liquidus temperatures were predicted by calculation of phase diagrams of the alloying metals. The brazing alloys were produced by gravity technique and melted using silicon carbide graphite crucible. The quality of the brazing alloys was analyzed by optical microscopy (OM), atomic absorption spectroscopy (AAS) and fourier transform infrared spectroscopy (FT-IR). Brazed joints were produced by torch method with a commercial flux. Brazing temperatures (liquidus) were tracked by a digital infrared/laser pyrometer. Some mechanical properties studied were tensile strength and hardness. Finally, brazed joints produced from the developed brazing alloys were compared to that produced from muntz brass. Six (6) brazing alloys were successfully developed. Zinc and manganese were the main components, to which were added; 3 to 4 %wt silver and 11 to15 %wt modifying element. The microstructure showed a typical eutectic structure with zinc-rich phase distributed uniformly in the matrix with a combination of different sizes of dendrite, rounded blocks of compounds and hypoeutectic structures. AAS results indicated minimal out-gassing of zinc and FT-IR results indicated very low presence of atmospheric gas. The range of brazing temperature for best results was recorded from 690.90 to 735.10 0C. The joints produced from the developed brazing alloys had acceptable strengths with improved stress-strain behaviour compared to muntz brass.

Keywords

• Brazing alloys
• Experimental design
• Mechanical properties mild steel
• Temperature
• Torch brazing
• Zinc