Study On Mechanical Properties And Failure Mechanisms Of Clinched And Clinch-bonded Joints In Aluminum-Lithium Alloy

With the increasing demand for Lightweight,more and more lightweight materials are used in various fields,such as automobile,aerospace and so on.Aluminum lithium alloy is one of the new lightweight materials,it's wide application brings new challenges to traditional connection technology.Based on the 1420 Aluminum lithium alloy as the research object,we used the new connection technology to make clinched joints and clinch-bonded hybrid joints.The mechanical properties of the joints were measured and the failure mechanism was analyzed,so as to provide a new method for the effective connection of 1420 Aluminum lithium alloy.In order to study the feasibility of the homogeneity/heterogeneity combination of 1420 Aluminum lithium alloy by using the clinch technique,we select titanium alloy(TA1),copper(H62)alloy and galvanized steel(DX52D+Z)to make 1420-1420?TA1-1420?H62-1420?DX52D+Z-1420 and 1420-DX52D+Z joints.The connection test proved the contact ability of 1420 Aluminum lithium alloy with other metals.The tensile strength and load-carrying capacity of the joint were measured by analyzing the joints' cross section and the static shear test on the joints.The 1420-1420 and the DX52D + Z-1420 combination were selected to carry out the connection test of the clinch-bonded hybrid technique.The joints were connected in two forms:single lap and the T-type.By comparing the corresponding single lap clinched joints and T-type clinched joints,the influence of the adhesive layer on the forming quality,tensile shear strength,failure displacement,failure mode and energy absorption of different forms of joints was studied.Micro SEM analysis was applied on the typical failure modes of joints,we analyze the types and characteristics of the joint fracture failure from the microscopic point of view.Results show that adhesive layer has greatly increased the biggest failure load,maximum displacement and energy absorption ability of clinched joints,and changed the failure mode of clinched joints.The influence of adhesive layer for T joint was less than the impact on the single lap joints.The fatigue behavior of 1420-1420 clinched joints and clinch-bonded hybrid joints at different stress levels was tested by dynamic fatigue test.The fatigue life curve of the joints was fitted by using the three-parameter power function expression,and the fatigue life and fatigue characteristics of the two joints were compared.The fatigue failure of the joints was analyzed by SEM scanning electron microscopy(SEM),in order to describe the characteristics of fatigue fracture,study the generation of fatigue crack source,find out the development process of crack,and analyze the effect of adhesive layer on the fatigue performance of clinched joints from microcosmic angle.Results show that clinch-bonded hybrid joints were sensitive to the change of fatigue stress levels;The fatigue life of clinch-bonded hybrid joints were better than clinched joints under a low stress state;Both two kinds of joint were neck fracture failure in a short fatigue life;Over the longer fatigue life area,fatigue fracture of clinched joints were the lower plate,fatigue fracture of clinch-bonded hybrid joints were clinched points in the lower plate;Two groups of fatigue fracture were ductile fracture and brittle fracture at the same time.