Porosity Formation Mechanisms and Controlling Technique for Laser Penetration Welding

2011 ◽  
Vol 287-290 ◽  
pp. 2191-2194 ◽  
Author(s):  
Wei Yao ◽  
Shui Li Gong
Keyword(s):  
Aluminum Alloy ◽  
Energy Distribution ◽  
Weld Pool ◽  
Laser Energy ◽  
Formation Mechanisms ◽  
Porosity Formation

The distribution and appearance characteristics of porosities in laser penetrated weld of aluminum alloy were observed, and the formation mechanisms of porosities were analyzed in detail, and the influences of twin spot laser energy distribution on porosities were investigated. It showed that there are two kinds of porosities, metallurgical and technologic porosities, in laser penetrated weld of aluminum alloy. The formation of metallurgical porosities is related to the separation, congregation and incorporation of hydrogen in the weld pool, while instantaneous instability of the keyhole is an essential reason for the occurrence of technologic porosities. Twin spot laser energy distribution can enlarge diameters of the opening and the root of the keyhole, improve fluctuating conditions of the wall of the keyhole, increase stability of the keyhole, and consequently decrease technologic porosities in number, but it has no obvious influence on metallurgical porosities.

Activation of the Si(100)/Cl2 Etching Reaction at High Cl2 Translational Energies

1991 ◽  
Vol 236 ◽  
Author(s):  
Francis X. Campos ◽  
Gabriela C. Weaver ◽  
Curtis J. Waltman ◽  
Stephen R. Leone
Keyword(s):  
Kinetic Energy ◽  
Film Thickness ◽  
Energy Distribution ◽  
Rate Increase ◽  
Laser Energy ◽  
Etching Rate ◽  
Laser Vaporization ◽  
Translational Energy ◽  
Break Surface ◽  
Broad Energy

AbstractExposing a Si(100) surface to a pulsed beam of neutral Cl2 with high translational energy results in etching at a rate faster than that seen with chlorine at thermal energies. The Cl2 beam used in these experiments is produced by laser vaporization of cryogenic films. It has a broad energy distribution which can be varied by changing laser energy and film thickness. Beams with mean energies as low as 0.4 eV result in etching =10 times faster than etching by thermal Cl2. When Cl2 beams are used which have considerable flux above 3 eV, the etching rate increases by a further factor of 3.6 ± 0.6. This rate increase, which occurs at energies just above the Si-Si bond energy, suggests that kinetic energy can be efficiently utilized to break surface bonds.

Porosity Formation after the Irradiation Termination of Laser

2013 ◽  
Vol 800 ◽  
pp. 201-204
Author(s):  
Wang Hong ◽  
Ling Yun Wang ◽  
Ri Sheng Li
Keyword(s):  
Surface Tension ◽  
Laser Welding ◽  
Continuous Wave ◽  
Laser Beams ◽  
Formation Mechanisms ◽  
Volume Of Fluid Method ◽  
Porosity Formation ◽  
Mode Laser ◽  
Melt Pool ◽  
Solidification Processes

Porosity is formed because of the keyhole collapse. The porosity formation is associated with the melt pool dynamics, the keyhole collapse and solidification processes. The objective of the paper is t to investigate porosity formation mechanisms and fluid flow in the melt pool using the volume of fluid method. The results indicate that the formation of porosity in continuous wave keyhole mode laser welding is associated to keyhole collapse, backfilling of liquid metal close the gas exit of the laser welding keyhole, surface tension of the gas/liquid interface play an important role in the backfilling downward to the keyhole right after laser beams left.Keywords: porosity; keyhole; collapse; welding; model

scholarly journals New Formation Mechanisms of Pores and Cracks in Micro-arc Oxidation Coatings on 6061 Aluminum Alloy with High Temperature Oxide Prefab Film

2021 ◽  
Vol 27 (1) ◽  
pp. 37-41
Author(s):  
Guo-rui WU ◽  
Dong-dong WANG ◽  
Xin-tong LIU ◽  
Mingjia WANG ◽  
Dong CHEN ◽  
...  
Keyword(s):  
Aluminum Alloy ◽  
High Temperature ◽  
Phase Interface ◽  
Oxide Phase ◽  
Formation Mechanisms ◽  
Coating Materials ◽  
6061 Aluminum Alloy ◽  
High Temperature Oxide ◽  
Micro Arc Oxidation ◽  
Temperature Oxide

Prior to micro-arc oxidation (MAO) treatment, a layer of high temperature oxide (HTO) prefab film was fabricated on the surface of 6061 aluminum alloy specimens. The formation mechanisms of the cracks and pores in the MAO coatings were investigated by means of Mg element as the tracer. The results showed that there were several different formation mechanisms for the pores and cracks formed in the MAO coatings as follows. Some of pores were attributed to the residual micro-discharge channels, and the others were attributed to the residual uncovered concave regions locating among the surrounding convex regions. The difference in oxide phase composition caused by the compositional fluctuations in the coating weakened the bond strength at the phase interface and resulted in forming cracks between every two convex regions. Some of cracks were resulted from the solidification and shrinkage of molten coating materials, and the others were resulted from the poor connection between every two convex regions. The surface morphology and the content of each element of the MAO coating were determined using scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS).

scholarly journals Research on Microhole Processing Technology Based on the Femtosecond-Laser Spiral Trepanning Method

2020 ◽  
Vol 10 (21) ◽  
pp. 7508
Author(s):  
Fengping Li ◽  
Guang Feng ◽  
Xiaojun Yang ◽  
Xiaogang Li ◽  
Guang Ma ◽  
...  
Keyword(s):  
Femtosecond Laser ◽  
Automotive Industry ◽  
Power Distribution ◽  
Normal Cone ◽  
Laser Energy ◽  
Processing Technology ◽  
Practical Significance ◽  
Formation Mechanisms ◽  
Spiral Scanning ◽  
Scanning Path

Microholes have crucial applications in aerospace, the automotive industry, and other industries. In this study, the microhole processing technology based on the femtosecond-laser spiral trepanning method was investigated. By adjusting the spiral scanning path, laser power distribution, and defocusing amount to control laser energy distribution, an inverted cone hole, straight hole, and normal cone hole were obtained finally. The morphology and element of the microhole were investigated by scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDX). The experimental results of the femtosecond-laser spiral trepanning method could achieve fewer impurities. Finally, the formation mechanisms of different microholes are explained in detail. The method is simpler and more efficient than the traditional microhole processing technology. The femtosecond-laser spiral trepanning method with controllable hole roundness, accuracy, and taper has important practical significance in microhole processing.

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