Microstructure and mechanical properties of friction welded cast and forged steel bars

Abstract

Friction welding has been represented as a technological solid-state joining processwidely used for dissimilar material combinations with high joint strength, short mass production time and low energy characteristics. This study investigates the factorsaffecting the joint performance of friction-welded joints, investment cast AISI 1050-AISI304 and forged AISI 1050-AISI 304 material pairs. The influence of manufacturingmethod of specimens under changing process parameters were examined both metallurgically and mechanically. An experimental set-up was designed and conducted forexperiments. Later, the tensile and microhardness tests were carried out and 23 factorialdesign was performed in order to evaluate effects of the process parameters.Statistical approach showed that friction pressure and forge pressure are the most viable parameters for forged parts while these are friction time, friction pressure and forgepressure for cast parts in order to maximize the tensile strength. The same procedure wasapplied to hardness values of the weld interface and it was found that friction time andfriction time are both effective in hardness, however, the increase in these parameters leads to decrease in hardness. Therefore it was concluded that higher values of friction time andfriction pressure are beneficial from the perspective of hardness whose high values cancreate notch effect at the interface. Additionally, correlation between the microstructureand mechanical properties was tested by macrographs, optical microstructure, SEM and EDS analysis. The recrystallization and mechanical mixed layer (MML) were observed inboth groups and it was confirmed that the reason of high hardness values is that ofmechanically mixed layer, oppositely, low hardness values belong to recrystallizationphenomena. Among these both groups, forged AISI 1050-AISI 304 friction weldments exhibited superior mechanical properties with lower hardness and higher tensile valuescompared to investment cast AISI 1050-AISI 304 group.