Defects Analysis And Ultrasonic Testing For AlSi10Mg Made By Selective Laser Melting

During the process of Selective Laser Melting(SLM),various types of micro-defects in the molding parts will be formed when under the influence of different process parameters.Under loading conditions,some micro-defects will turn into the damage-type defects.Therefore,it is necessary to use Non-Destructive Testing(NDT)technology to analyze the features of defects and evaluate their effects on structural reliability.This thesis presents a focused study of the internal microstructure and defects of SLM molding parts,and which proposes use ultrasonic technology to test molding parts.Meanwhile,the effect of microstructure on ultrasonic field was analyzed.Based on the special microstructure of molding parts,the Transmit-Receive probe(TR probe)for testing AlSi10 Mg molding parts was studied and designed,and with simulations and experiments carried out,whose performance was also been tested.Details of this work are as follows:(1)This thesis reviewed the current researches of SLM molding parts.The microstructures of AlSi10 Mg molding parts were studied,with the cause,size and spatial distribution of common micro-defects in the molding parts,and the feasibility of ultrasonic testing been analyzed.(2)In view of the special microstructure of molding parts,this thesis proposed researching and developing a new TR probe.Took the TR probe as the research object,and based on the multi-Gaussian beam model,the influences of major parameters to design TR probe on sound field were simulated by Matlab software.After being optimized by simulation,the final optimal parameters of probe are as follows: the probe frequency is 4MHz,the radius of crystal is 3mm,the angle of crystal is 10°,the wedge height is 10 mm,the distance between crystals is 7.5mm.(3)Through established different depth and different size of flat-bottomed holes in the molding parts and done qualitative testing,the echo wave signals of the TR probe were obtained by simulation based on the mathematical model of probe detection echo wave.Results show the TR probe can test each defects effective,and compared the simulation outputs with experiment dates,the results show a high accuracy with a 6.1% average deviation.(4)The quantitative comparative analysis of flat-bottomed crack defects in AlSi10 Mg molding parts proved the good performance of TR probes,showing that the TR probe has a greater advantage in detecting near-surface defects with 4% error rate of crack length measurement,which is far less than the 17.8% error rate of the direct probe.