| The self-propagation exothermic reaction of Al/Ti nano-multilayers is of great interest because of its rapid reaction and high heat release,and Al/Ti nano-multilayers is a potential heat source for the connection of micro and nano units,so it is important to study the mechanical properties of welded components for its application.Based on this,this thesis used molecular dynamics simulation to study the self-propagation exothermic reaction of Al/Ti nano-multilayer film,and through the exothermic reaction to achieve the connection between aluminum and titanium heterogeneous metals the mechanical properties and microscopic deformation mechanism of the post-welded components,for the development of Al/Ti nano-multilayer film self-propagation welding.The mechanical properties and microscopic deformation mechanism of the post-welded components were analyzed to provide theoretical support for the development of the Al Ti nano-multilayer film self-propagation welding process.Firstly,molecular dynamics simulations were used to study the exothermic reaction of Al/Ti nano-multilayers and to realize the connection of Al/Ti dissimilar metal.The effectiveness of self-propagation welding was verified by comparing the mechanical properties of Al/Ti components before and after welding.The results of numerical analysis showed that the Young’s modulus of the welded components was27.3% higher than that of single-crystal aluminum.The application of Al/Ti nanomultilayers in welding can effectively improve the mechanical properties of the welded components.Secondly,the orthogonal experimental analysis method and the control variable method were used to study the effects of five welding process factors,such as the periods of Al/Ti nano-multilayer film,initial holding temperature,system pressure,ignition temperature,and heating rate on the mechanical properties and deformation mechanism of aluminum-titanium welded components under tensile loading.The optimal combination of welding conditions for the Al/Ti nano-multilayer film periods is 3,the initial holding temperature is 350 K,the ignition temperature is 790 K,the system pressure is 50.1 MPa,the heating rate is 6 K/ps.Each level of factors on the yield strength of the welded components has a impact order: Al/Ti nano-multilayer film periods > initial holding temperature > system pressure > ignition temperature >heating rate.The yield strength of the welded components was reduced from 6.23 GPa to 4.07 GPa and Young’s modulus from 87.41 GPa to 65.21 GPa with the increase of the number of layers.When the period is 3,the best mechanical properties are achieved for the welded component.Finally,the effects of tensile temperature,modulation ratio and strain rate on the mechanical properties of Al/Ti post-welded components were analyzed and studied.With the increase of tensile temperature,the yield strength of welded components decreased from 6.23 GPa to 2.25 GPa and Young’s modulus decreased from 87.41 GPa to 53.98 GPa,all showing a decreasing linear trend.The best mechanical properties of the welded components were observed when the tensile temperature was 100 K.As the modulation ratio of Al/Ti nano-multilayer film increases,the yield strength of the postwelded members tends to increase and then decrease.When the modulation ratio is 6/3,the total length of dislocation lines inside the welded component reaches the maximum value of 2245 nm,and the total length of fixed dislocation reaches the maximum value of 851 nm.The fixed dislocation can effectively prevent the slippage of dislocation inside the welded component and improve the yield strength of the material.As the strain rate decreases,the yield strength of the post-welded component reduces from7.84 GPa to 3.87 GPa.The sensitivity of the yield strength to the internal dislocation response of the post-welded component is high at high strain rates,and the yield strength of the material reaches a maximum value of 7.84 GPa. |
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