Mechanical Performance Analyze Of Flame Hardening Clinching Joints

With the advent of energy crisis and environmental pollution, which result in these issues become more and more serious, therefore, energy conservation and emission reduction had drawn the global attention. Lightweight structure is a significant method to accomplish the goals what are energy conservation and emission reduction in the industrial field. Thus light metal was widely used in variety of product manufacturing, In order to better join the light metal, brand new interconnection technique was in urgent to develop. Clinching is developing rapidly under this backdrop.Researchers found that the dynamic fatigue performance of clinched joints was superior to the conventional spot welding, but the static strength of the single point clinched joints is only 75% of the spot welding. Clinched joints were the study object of this paper. Clinched joints had local thermal treatment by setting up a flame hardening test platform. All works were to improve integrated mechanical of the clinched joints. Specific study was as follows.1) The experiment of local thermal treatment on clinched joints made by cold-rolled steel and galvanized steel was conducted on the self built flame hardening test platform. After that the static strength of two group joints had or no thermal treatments were tested. Test results show that flame hardening could improve static mechanical properties effectively. It also had an effect on the failure modes of the joints. Then the metallographic analysis was taken on cold-rolled steel joints with flame hardening. Results show that a large number of lath marten site appeared after thermal treatment.2) Fatigue performance of the cold-rolled steel clinched joints with and without flame hardening was tested. The test results exhibit that flame hardening could enhance the joints fatigue performance when the joints under high stress, but the joints fatigue performance was weaken after flame hardening when the joints under low stress.3) To analyze fatigue fracture what was adopted scanning electron microscope (SEM). Results indicate that fatigue fracture characteristic of joints without flame hardening present ductile microvoid at the crack initiation site. At crack develop site, fracture characteristic was quasi-cleavage-like. High stress level fatigue fracture characteristic of joints after flame hardening had the same character as fracture of joints without flame hardening. But the fracture characteristic of flame hardening joints under low stress level load only had quasi-cleavage-like character.