Influence of CO_2 laser welding parameters on the microstructure, metallurgy, and mechanical properties of Mg-Al alloys

This study investigated the microstructural characteristics, metallurgy, microhardness, and tensile strength of AZ31 and AZ61 magnesium alloy weldments, fabricated in a CO2 laser welding process with the adjustment of various parameters. The results show that the AZ31 weldment contains equiaxed grains within the fusion zone （FZ）. By contrast, the FZ of the AZ61 weldment contains refined cellular grains and the partially melted zone （PMZ） contains bulk grains. We infer that the difference in aluminum content between the two magne-sium alloys results in different supercooling rates and solid grain structures. For both weldments, the ultimate tensile strength （UTS） de-creases following the CO2 laser welding process. However, no significant difference is noted between the UTS of the two weldments, sug-gesting that tensile strength is insensitive to the Al content of the magnesium alloy. The CO2 laser welding process is shown to increase the microhardness of both magnesium alloys. Furthermore, grain refinement is responsible for the maximum hardness in the FZ of both weld-ments. The AZ61 weldment has a higher content of Al, resulting in a greater grain refinement.

Geographical Traceability of Clinacanthus nutans with Near-Infrared Pectroscopy and Chemometrics

In this study, a seed origin discrimination model for Clinacanthus nutans was developed. First, 81 C. nutans samples from three seed origin locations were collected, and their Near-Infrared (NIR) spectra were obtained. Next, Principal Component Analysis (PCA) was performed on the NIR spectra of the 81 C. nutans samples. Then, MSC (multiplicative scatter correction), SNV (standard normal variate), first derivative, and second derivative pre-treatments of the C. nutans spectra were performed and combined with the Support Vector Machine (SVM) algorithm for modelling and analysis. Among these methods, first-order derivative pre-treatment achieved the best SVM model effectiveness, with a training set accuracy of 93.44% (57/61) and a test set accuracy of 85.00% (17/20). In order to further improve the discrimination accuracy of the model, three optimization algorithms Grid Search (GS), Genetic Algorithm (GA), and Particle Swarm Optimization (PSO) were employed to identify the best c and g parameters for the SVM model. The results demonstrated that the PSO optimization algorithm yielded the best parameters of c = 0.8343, g = 57.8741, with corresponding model training set the accuracy of 96.36% (60/61) and test set the accuracy of 95.00% (20/21). Therefore, developing a seed origin classification model for C. nutans based on NIR spectroscopy combined with chemometrics is feasible and has the advantages of being simple, rapid, and green.

Generic nonlinear error compensation algorithm for phase measuring profilometry

In this Letter,the periodical errors,which are caused by the nonlinear effect of the commercial projector and camera,are analyzed as a more generic single-coefficient model.The probability density function of the wrapped phase distributions is used as a tool to find the compensation coefficient.When the compensation coefficient is detected,on the premise of ensuring accuracy,a correlation algorithm process is used to replace the traditional iterative process.Therefore,the proposed algorithm improves the efficiency of coefficient detection dramatically.Both computer simulation and experiment show the effectiveness of this method.

Spherical distribution structure of the semiconductor laser diode stack for pumping

A semiconductor laser diode stack is used for pumping and 8 semiconductor laser diode arrays of the stack are put on a sphere,and the output of every bar is specially off-axis compressed to realize high coupling efficiency.The output beam of this semiconductor laser diode stack is shaped by a hollow duct to the laser active medium.The efficiency of the hollow light pipe,which is used for semiconductor laser diode stack coupling,is analyzed by geometric optics and ray tracing.Geometric optics analysis diagnoses the reasons for coupling loss and guides the design of the structure.Ray tracing analyzes the relation between the structural parameters and the output characteristics of this pumping system,and guides parameter optimization.Simulation and analysis results show that putting the semiconductor laser diode arrays on a spherical surface can increase coupling efficiency, reduce the optimum duct length and improve the output energy field distribution.