Study The Relationship Between Microstructure Of Heat Affected Zone And Mechanical Properties Of GH4169 Alloy

GH4169 alloy is a kind of precipitated reinforced superalloy.Due to the good strength and toughness,weldability,and fatigue and fracture toughness,it has widely used in aerospace,shipbuilding,chemical industry and other industries.For the ring rolling part of GH4169 alloy,considering the cost of production,has used the technology of flash welding to produce.Flash welding technology has advantages in terms of welding efficiency,quality control and profile size.But,there are few reports about the relationship between microstructure and mechanical properties of welded joints.For this problem,it is necessary to systematically study the microstructure evolution and mechanical behavior of the GH4169 alloy welded joint under two typical temperature gradients.Two typical heat treatment processes are used to change the microstructure of welded joints,and restore the tensile properties.Meanwhile,it provides reference and technical guidance for producing high-performance weldment,and achieving no or less welding defects.(1)The welding temperature gradient is controlled by the heat storage and heat transfer efficiency of GH4169 alloy.The mechanism of microstructure evolution of welding seam(WS)and heat affected zone(HAZ)were characterized by OM,SEM,TEM and EBSD.It is found that the gentle temperature gradient with high average temperature can effectively prevent the welding defects,but has resulted in the coarsening of grains and the precipitation and growth of carbides.Thus,the plasticity and strength of welded joint are significantly reduced.(2)During the flash welding,the welding heat is derived from the liquefaction and gasification of the two welding surfaces under the action of high density current.Then,the temperature gradient forms at the welded joint by the heat transfer,in which decreases from the welding surface to matrix.The moderate temperature gradient can obtain high-quality weldments.The reduction of hardness is significantly affected by the dissolution of strengthening phase in GH4169 alloy.Therefore,the hardness distribution of welding zone can be used to measure the temperature gradient,and produce high-quality weldments.Meanwhile,it is also a simple and rapid method to evaluate the welding quality.(3)The effect of various solid solution and aging processes on the microstructure and mechanical properties of welded joints were systematically studied.The strength and plasticity of welded joint at the 980 ? solution and aging treatment are slightly higher than the base metal.The effect of the solid solution temperature on the growth rate of grain in the heat affected zone(HAZ)was calculated by the Beck equation.It is found that the index of grain growth at welding seam(WS)was the lowest,and the largest index appeared near the weld seam.The influence of solution temperature and holding time on the precipitation behavior of ? phase in heat affected zone(HAZ)is explored.The precipitation of ? phase at welded joint has a gradient trend,which is gradually decreased from the edge of welding seam(WS)to base metal.Its consistent with the increasing trend of grain size.(4)The effect of low temperature and solution aging treatment on the microstructure and mechanical properties of welded joints was studied.It is found that the strength does not change with the low temperature time,but the plasticity gradually decreased.The effect of residual strain energy in the heat affected zone(HAZ)on the degree of static recrystallization was also discussed.