Yongkang Zhang

Laser processing has been used as a surface preparation before adhesive bonding, which significantly improves the adhesion between the adhesive and the substrates. In this work, a pulsed fiber laser was used to process different microgrooves in the bonding region of a Ti6Al4V substrate. First, the pulse energy was optimized, and then the effects of the microgroove parameters (groove pattern, depth, and distance) on the surface roughness of the substrate and on the shear strength and failure mode of the adhesive joints were studied using a single factor experimental design. The results show that when the pulse energy is greater than 63 μJ, a significant amount of molten residue is generated around the groove. The parallel groove is the most beneficial to improve the shear strength when the groove direction is 90° (when the groove is perpendicular to the loading direction). In contrast, cross grooves easily form pores that are not filled with adhesive, which weakens the shear strength. The shear strength was observed to decrease for greater groove distances and increase with the groove depth. The maximum shear strength of the adhesively bonded joint after laser processing is about 29.71 MPa, which is an increase of 140% compared with that by surface grinder polishing.

While parts can be repaired via arc welding (AW), it is usually necessary to add some types of excitation method to improve the mechanical properties of the cladded layer. Here, the arc welding‐laser shock forging (AW‐LSF) was used to repair Q235 steel pipes (Fe‐Cr‐C alloy was used as the cladding material). The effects of the welding current (WC), welding speed (WS), and laser shock frequency (LSF) on the geometry and microhardness of the weld bead were studied. The AW‐LSF and AW repair processes were compared. The results demonstrate that the bead width (W) and penetration depth (D) increase with the WC, while the weld height (H) decreases with the WC. The H, W, and D all decrease with the WS; W and D increase with the LSF; and H decreases with the LSF. As the WC increases, the hardness of the fusion zone (FZ) and partial fusion zone (PFZ) decreases significantly, while the hardness of the heat‐affected zone (HAZ) remains nearly unchanged. As the WS increases, the hardness of the PFZ decreases, while the hardness of the FZ and HAZ remains nearly unchanged. With the increase of the LSF, the hardness of the PFZ, FZ, and HAZ increases. Compared with AW, the AW‐LSF can reduce the cladded layer crystal grain size, increase the hardness, and improve the sliding wear resistance.

为了研究强脉冲激光在镁合金中诱导冲击波的衰减,采用Nd:Glass脉冲激光(1054 nm,23 ns)对AZ31B变形镁合金试样表面进行冲击,并利用响应快、测量范围大的PVDF压电膜传感器以及示波器实时测量了强脉冲激光在镁合金靶中诱导激光冲击波的相对压力.根据冲击波每次在靶材背面反射时,所经过距离的不同得到激光冲击波在镁合金中的衰减规律.结果表明,在激光能量为5J的强脉冲激光作用下,镁合金中冲击波衰减的平均速度为5.83×103 m/s,与镁合金中应力波纵波的传播速度相符;强脉冲激光诱导冲击波在镁合金中是以指数规律衰减的.试验所得分析结果对激光冲击强化镁合金的应用具有重要意义.

The laser shock induced stress wave is described and measured with a polyvinylidene fluoride (PVDF) transducer. A principle for selecting laser parameters is proposed. A small sized laser with a high power is used for Laser Shock Processing (LSP). The fatigue life of the aluminum alloy 2024T62 is greatly improved after LSP. With 95% confidence, the mean fatigue life of LSP specimens is 4.5–9.8 times that of unshocked ones. The fatigue and fracture resistance mechanisms of LSP such as the variation of the surface hardness, the microstructure and the fracture section of specimens before and after LSP are analyzed. [S0094-4289(00)01601-7]