Y. X. Huang

Microstructural Characteristics and Mechanical Properties of 7050-T7451 Aluminum Alloy Friction Stir-Welded Joints

The ultra-high-strength Al-Zn-Mg-Cu alloy, 7050-T7451, was friction stir welded at a constant tool rotation speed of 600 rpm. Defect-free welds were successfully obtained at a welding speed of 100 mm/min, but lack-of-penetration defect was formed at a welding speed of 400 mm/min. The as-received material was mainly composed of coarse-deformed grains with some fine recrystallized grains. Fine equiaxed, dynamic, recrystallized grains were developed in the stir zone, and elongated grains were formed in the thermomechanically affected zone with dynamic recovered subgrains. Grain sizes in different regions of friction stir-welded joints varied depending on the welding speed. The sizes and distributions of precipitates changed in different regions of the joint, and wider precipitation free zone was developed in the heat-affected zone compared to that in the base material. Hardness of the heat-affected zone was obviously lower than that of the base material, and the softening region width was related to the welding speed. The tensile strength of the defect-free joints increased with the increasing welding speed, while the lack-of-penetration defect greatly reduced the tensile strength. The tensile fracture path was significantly influenced by the position and orientation of lack-of-penetration defect.

Investigation of the Correlation Between Plasma Electron Temperature and Quality of Laser Additive Manufacturing Process

In this paper, a spectral diagnosis method was reported to explore the temperature characteristic of plasma and detect the forming quality in laser additive manufacturing. The spectral data were collected by the spectrum acquisition system under different processing parameters. The plasma temperatures under different processing conditions were calculated using Boltzmann plot of six neutral iron lines between 375 nm and 390 nm, and the influence relationships between laser power, powder feeding rate, traverse speed, cladding layer and plasma temperature were found. Meanwhile, the time domain diagrams (the relationship between the temperature and time) corresponding to the process were established, in which temperatures were respectively calculated by Boltzmann double-line method and Boltzmann plot method, to analyze the correlation between temperature fluctuation and the forming defects. It was found that the results from Boltzmann plot method could reflect the generated defects more clearly.

Effect of Rotation Speed on the Microstructure and Mechanical Properties of Friction-Stir-Welded CuSn6 Tin Bronze

Four-mm-thick CuSn6 tin bronze plates were friction stir welded at a constant tool traverse speed of 100xa0mmxa0min−1. Favorable joints could be obtained with rotation speeds ranging from 600 to 1000xa0revxa0min−1, and groove was found on the surface of the joint under 400xa0revxa0min−1. The microstructure of the weld nugget zone was characterized by equiaxed recrystallized grains with heterogeneity along the thickness direction. Moreover, the grain size of the thermo-mechanically affected zone and stir zone increased with the increase in rotation speed. Hardness of the stir zone was higher than that of other zones due to microstructural refinement. There was little change in tensile properties of the defect-free welded joints. During tensile test, all of the defect-free joints were fractured at heat-affected zone with typical plastic fracture.

Process Parameter Optimization in Refill Friction Spot Welding of 6061 Aluminum Alloys Using Response Surface Methodology

Abstract6061-T6 aluminum alloy joint was fabricated by refill friction stir spot welding (RFSSW) on which three process parameters of tool rotation speed, sleeve moving rate, and plunge depth make an important effect. The response surface methodology (RSM) was applied to establish a mathematical model to study the effect of process parameters on lap shear fracture load (LSFL) of the RFSSWed joints which were performed in Box–Behnken designs with three factors, three levels and 15 runs. Analysis of variance used to check the adequacy of the developed model indicates that the mathematical model is significant. LSFL increases with the increase in tool rotation speed, sleeve plunge depth, and sleeve moving rate to maximum and then decreases. Sleeve plunge depth makes the most effect on LSFL in all process parameters. The RFSSW process parameters were also optimized using RSM to predict maximize LSFL. The joint produced using a tool rotational speed of 1506xa0rpm, sleeve moving rate of 1.01xa0mm/s and sleeve plunge depth of 2.46xa0mm displays higher LSFL.n