Study Of Micromechanical Behavior About High Silicon Aluminum Alloys Based On SEM-DIC Method

High silicon aluminum alloys have broad application prospects in the field of electronic packaging because of its low density,low coefficient of thermal expansion(CTE)and stable thermal mechanical performance.However,electronic packaging structures tend to be damaged by thermal loads and complex mechanical loads during operation,so it is of great significance to accurately measure its high temperature micro mechanical behavior.Previous studies have shown less analysis of the mechanical behavior of high silicon aluminum alloys at high temperatures.The relationship between the microstructure and deformation of the alloy cannot be explained,and it is difficult to determine the relationship between the microscopic mechanism of the alloy and the mechanical properties.Digital image correlation(DIC)has the characteristics of full field measurement,non-contact and strong anti-interference ability.It can be combined with microscopy equipment such as scanning electron microscope(SEM)to realize deformation at micro scale,and it has great advantages in the study of mechanical properties of micro scale.In this dissertation,based on the DIC method and SEM high temperature in-situ loading system,the micro-mechanical behaviors of high silicon aluminum alloys with different silicon contents of Al-27%Si,Al-42%Si and Al-60%Si were studied.This article has mainly completed the following works:Firstly,based on the DIC method,a high temperature in-situ loading system under SEM was built.The metallographic samples of three high silicon aluminum alloys were designed and prepared.The natural features of the sample surface were used as the speckle pattern for DIC deformation calculation.A method for calibrating the SEM image noise is proposed to optimize the parameter setting of the SEM,which greatly reduces the noise in the SEM image.The reliability of SEM-DIC method was verified by using copper and pure aluminum samples,and the accuracy of the system under different magnifications was verified by zero deformation experiment.The results show that this method has high precision and can be used to measure the micro-scale deformation measurement of high-silicon aluminum alloy at high temperature.Secondly,based on SEM-DIC method,the tensile mechanical behaviors of three high silicon aluminum alloys,Al-27%Si,Al-42%Si and Al-60%Si,were studied at different temperatures.The results show that the silicon content and temperature have a significant effect on the high temperature tensile mechanical behavior of the alloy.The tensile mechanical properties of three alloys decrease with the increase of temperature,the decreasing trend of Al-27%Si is the most obvious,and the resistance of Al-60%Si is the worst.The crack of Al-27%Si is mainly initiated in the aluminum matrix,and the cracks of Al-42%Si and Al-60%Si are mainly initiated in the silicon phase.The silicon content is the key factor affecting the tensile fracture mechanism of high-silicon aluminum alloy.With the increase of silicon content,the main tensile fracture mechanism of the alloy changes from the ductile fracture of the aluminum phase to the brittle fracture of the silicon phase.The temperature has little effect on the micro-scale tensile deformation field distribution and tensile fracture mechanism of high-silicon aluminum alloy,and its influence degree decreases with the increase of silicon content.Thirdly,based on SEM-DIC method,the bending mechanical behaviors of three high silicon aluminum alloys,Al-27%Si,Al-42%Si and Al-60%Si,were studied at room temperature.The results show that the bending mechanical properties of high-silicon aluminum alloy mainly depend on the content of silicon.With the increase of silicon content,the ability of the alloy to resist bending failure is reduced,and the ability to resist bending deformation is enhanced.The three alloys have lower tensile failure resistance than compression resistance under bending load.The crack of Al-27%Si is mainly initiated in the aluminum matrix,and the cracks of Al-42%Si and Al-60%Si are mainly initiated in the silicon phase.As the silicon content increases,the main bending fracture mode of high silicon aluminum alloy gradually changes from the ductile fracture of the aluminum phase to the brittle fracture of the silicon phase.Finally,the distribution of micro-local thermal deformation of high silicon aluminum alloy was studied by SEM-DIC method and simulation method.The results show that the silicon content is the key factor affecting the CTE of high silicon aluminum alloy.With the increase of silicon content,the CTE of high silicon aluminum alloy decreases significantly.The SEM-DIC method has higher reliability for measuring the CTE of Al-27%Si and Al-42%Si alloys,and the measured value of CTE in the x direction is more accurate.The measurement error of this method increases as the silicon content increases.The results of the finite element simulation method show that the silicon content and particle size have a significant effect on the microscopic thermal deformation distribution of the alloy.As the silicon content increases,the average thermal strain of the alloy decreases,the strain gradient increases,and the maximum strain occurs at the interface of the two phases.As the silicon content increases,the thermal deformation generated inside the alloy is greater,and failure damage is more likely to occur under the action of thermal load.