Low Speed Laser Welding of Aluminium Alloys Using Single-Mode Fiber Lasers

Abstract

Background and Reviews Aluminium AlloysAluminium alloys can be separated into two major categories: Non heat-treatable and heattreatable. The initial strength of non heat-treatable alloys depends primarily upon the hardening effect of alloying elements such as silicon, iron, manganese and magnesium. The non heat-treatable alloys are mainly found in 1xxx, 3xxx, 4xxx and 5xxx series. Additional strength is usually achieved by solid-solution strengthening or strain hardening. The initial strength of heat-treatable alloys depends upon the alloy composition, just like the non heat-treatable alloys. In order to improve their mechanical properties they need to undergo solution heat treating and quenching followed by either natural or artificial aging (precipitation hardening). This treatment involves maintaining the work piece at an elevated temperature, followed by controlled cooling in order to achieve maximum hardening. The heat-treatable alloys are found primarily in the 2xxx, 6xxx and 7xxx alloy series (ibid). The 7xxx series alloys contain zinc in amounts between 4 and 8 % and magnesium in amounts between 1 and 3 %. Both have high solid solubility in aluminium. The addition of www.intechopen.com Low speed laser welding of aluminium alloys using single-mode iber lasers 49 magnesium produces a marked increase in precipitation hardening characteristics. Copper additions between 1 and 2 % increase the strength by solid solution hardening, and form the basis of high strength aircraft alloys. The addition of chromium, typically up to 0.3 %, improves stress corrosion cracking resistance. The 7xxx series alloys are predominantly used in aerospace applications, 7075-T6 being the principal high strength aircraft alloy (Ion, 2000). This chapter will focus on fiber laser welding of 7075-T6 because of its predominant use in aircraft components.

The Effect of Process Parameters on the Microstructure and Mechanical Properties of AW5083 Aluminum Laser Weld Joints

“…Wu et al [51] found that the surface tension of the molten metal and the recoil pressure caused by evaporation were responsible for the spatter formation. The oxide layer formation on the surface of the molten metal is associated with the high affinity of Al to O 2 , which can prevent the escape of bubbles from the weld metal [52,53].…”

Keyhole-induced porosity in laser-arc hybrid welded aluminum

“…Also, there is some evidence that the bubble velocity is suppressed during turbulent flow [24]. The solidification rate during laser welding of aluminum has been suggested to be up to 10 5°C s −1 or higher [25,26]. Under this condition, the weld metal solidifies more rapidly than the possible rise velocity of the gas bubbles formed during keyhole collapse, resulting in severe porosity in the weld metal.…”

Effect of shielding gas on the properties of CP titanium Grade 2 laser weld joints

“…Molten pool instabilities in the root area may cause gas bubbles. The high affinity of titanium to oxygen can give rise to the formation of an oxide layer on the melt very quickly, which impedes gas bubbles escape [34,35]. In deep penetration welding, the weld depth is increased, but due to the formation of the gaseous keyhole, the risk of process defects is increased.…”