Cr-zr-cu Copper Alloy Tig Welding And Post Weld Heat Treatment On The Joint Microstructure And Properties,

Cr-Zr-Cu copper alloy is a precipitation hardening alloy with high strength, high conductivity, age-hardening type alloy, there are rarely research and application about weldability of this material. In this paper, Cr-Zr-Cu copper alloy thin plate with thickness of 5mm was researched by the method of gas manual argon tungsten arc welding (GTAW) and post weld heat treatment.Experimental results show that good shaped and good fusion welding could be got by a high preheating temperature(500℃) and large-current(300A) fast-welding(14cm/min). Metallographic observation, hardness and electrical conductivity test result show that microstructure in the equiaxed crystal zone is coarseαphase equiaxed grain, columnar structure is near the fusion line, HAZ is very wide, and grains of HAZ (heat-affected zone) are grow severely, it turns twin structure with single-phaseα.. Precipitation of compounds exist in the grain boundary and inner of grain structure; because of the coarse weld microstructure and uneven distribution of alloying elements, conductivity of the joint declines seriously, welding seam's conductivity is lower than HAZ's, conductivity of columnar crystal zone is the lowest. Welding joint's hardness is also decreased, And HAZ's hardness is relatively low.When the HT (heat treatment) temperature is high (950℃) , the grains grow serious. Cr, Zr and other elements precipitates along grain boundary with the form of compounds seriously because of overburning. As the homogenization of alloying elements in the weld metal and the release of welding residual stress, weld electrical conductivity is enhanced. However, weld electrical conductivity increase is limited for the reason that grain growth and alloying elements precipitation along grain boundary, and it even dropped in some regions. The conductivity increase will be significant if the HT time is long. Hardness has generally decreased as the result of grain growth and alloying elements precipitation along grain boundary after heat treatment.Grain growth of recrystallization won't happenned under the conditiong of a relatively low HT temperature (470℃) . Supersaturated alloy in the weld is precipitated dispersly in the coarse grain of center equiaxial crystal zone and columnar crystal zone, and it won't segregate along the boundary. Precipitated phase was shaped like a net in the grain if the heat preservation could be kept for a long time. Welded joints'conductivity is improved by HT. However, with the HT time was prolonged, conductivity couldn't be enhanced. Microhardness of weld has improved greatly after heat treatment. As microstructure does not change and strengthening phase precipitates not abviously in a certern distance away from weld center, the microhardness hardly increased.