Establishment Of Constitutive Equation Of Tin-based Solder Under Extreme Temperature Environment

Deep space exploration has played an important role in space exploration and aerospace activities nowadays,and it is of great significance to the development of human civilization.The electronic system is an important part of the deep space detector,and the solder joints are one of the most fragile and important parts of the electronic system.The failure of electronic equipment caused by the failure of solder j oints will affect the mission of deep space exploration and even lead to failure.In the deep space environment,the extreme temperature of the detector affects detectoe a lot.The life prediction and estimation of the solder joints in the extreme low temperature environment are critical to the success of the entire detection mission.Therefore,it is necessary to control the Snbased solder that is often used in electronic equipment.The mechanical behavior and constitutive equations under extreme low temperature environment are studied.In this paper,Sn37Pb solder and SAC305 solder had undergone uniaxial tensile mechanical tests at different temperatures and strain rates.Under different temperature conditions,the tensile mechanical properties of the two solders could be divided into three zones by the shape of the tensile curve.The temperature is divided into zone ?—creep zone,zone ?—ductile zone,and zone ?—brittleness from high to low.The tensile mechanics curves of the two solders in the creep zone change obviously with the tensile rate.The faster the tensile rate,the higher the strength of the material,the lower the elongation.The relationship between the tensile rate and mechanical properties of the material in the tough and brittle zone are less affected.Comparing the mechanical performance curves and fracture morphology of the two solders under extreme low temperature environment,the tensile mechanical curves of Sn37Pb are roughly the same at-196? and-186?,which were divided into two different stages,the first stage of stress shows the strain rate increases faster,the second segment is slower.The fracture of the brazing filler metal was densely distributed with "dimple"structures,indicating that although the material fracture mode was biased towards brittle fracture,there was still a structure with ductile fracture mechanics characteristics.The mechanical performance curve of SAC305 solder had only one stage,and the fracture was the combined effect of transgranular fracture and intergranular fracture,which is a complete brittle fracture.At-170? and-180?,the two solders exhibited brittle fracture characteristics at high tensile rates,and exhibited a curve characteristic of ductile and brittle mixed at low tensile rates.The material had the characteristics of a ductile and brittle hybrid port at low strain rates.Based on the data obtained from the Charpy impact test,the relationship between the ductile-brittle transition temperature and the strain rate of the Sn-based solder is summarized.When Sn37Pb solder was brittle fracture,there were micro-cracks distributed on the fracture surface.Based on this situation,the Weibull distribution damage constitutive model was selected.Integrating the mechanical properties of the brazing filler metal and the changing trend of the mechanical properties parameters with the ambient temperature and the tensile rate,the brazing filler metal had a strain rate correlation at-186?,which defines the rate damage coefficient D(?),established a relationship with the maximum strain rate ?_f,and obtained an improved constitutive equation based on the Weibull distribution model.Four parameters including elastic modulus E,brittleness index n,rate damage coefficient D(?)and reference elongation rate ?_f~0 were obtained by fitting.The brittleness index n and the rate damage coefficient of the brazing filler metal D(?)were strain rate sensitive,and both increase with the increase of the strain rate,indicating that the strain The larger the rate,the smaller the elongation of the solder,and the deeper the brittle fracture.Substitute the parameters into the constitutive equation of the brittle stage to test.The faster the stretching rate,the more accurate the fitting,while the slower the strain rate,the worse the fitting effect.