Aluminum alloys, are lightweight, possess good thermal and electrical conductivity, and are relatively inexpensive to work with. Therefore, it’s no surprise that they are being used with increased frequency in product manufacturing applications ranging from batteries and electronics packaging, to automotive components and consumer goods packaging. Laser welding aluminum, however, is more difficult than welding steels for three key reasons: high reflectivity, surface oxide layer, and volatile alloying elements.
- High reflectivity - Aluminum is highly reflective to 1064 or 1070nm wavelength Nd:YAG and fiber lasers, meaning that high power density is needed to overcome this reflectivity and enable the laser to deliver heat to the part.
- Surface Oxide layer - Removing the oxide layer by either mechanical or chemical means ensures that dirt and contaminants that may be in the oxide layer are removed. Note that plating should be avoided in the welding area as it typically causes weld cracking.
- Material - Material selection is key in avoiding the more volatile alloying elements which can cause excess porosity and cracking, typical good material selections are 1050, 2219, 3003, 5052, 6061 & 4047. Note that 6061 is only weldable in combination with 4047 (though 4043 can be used) due to the silicon content of the 4047 alloy that prevents cracking.
Hermetic Welding of RF/Microwave Packages
The required material combination is 6061 for the body and 4047 for the lid. The joint geometry should be butt joint such that the penetration requirements are minimized. Typically in these applications a 500 or 600 micron spot size is used to ensure joint coverage and weld stability.
When sourcing different material alloys for components that require welding it’s important to ensure that the alloys are weldable not only to themselves but also with the other alloy.
As an example, consider 3003 and 5052, both weldable to themselves, however, if joined together the alloying elements create a condition that increases crack sensitivity, as shown in Figure 3:
Some good background reading on alloy mixing - albeit not for laser welding - is Dudas, J.H and Collins, F.R. The Welding Journal, 45, 241s, 1966.