Laser welding has been used for years to join materials or perform engraving. It is commonly used in manufacturing and has become common enough to see laser welders at mall jewelry stalls. This post covers laser welding analysis including two specific examples—a titanium pacemaker and an iron/aluminum weld.
The key to precise laser welding is to get the correct laser, laser power, and duration to get the appropriate weld result. In addition, process parameters like a precise weld depth are used to ensure the weld interconnection is deep enough. Still, the laser does not go through the materials being joined. Therefore, minimizing the heat-affected zone (area of grains structure change) and eliminating gaps and holes are critical in many markets we serve.
Medical device manufacturers that weld surgical devices cannot afford to let a weld fail due to a flawed process. A failure could mean a fatality in the surgical suite or after implantation.
EV battery makers and solar panel makers need a sold weld to guarantee good electrical contact while providing lasting reliability in extreme environments. EV battery manufacturers can also not afford leakages of battery materials as these materials can explode when exposed to an open environment.
Laser Welding Your Samples
JH Analytical works with its customers to characterize their welding process. For example, we can analyze the depth of the weld into the joint, the amount of the materials that are “mixed” during the welding process, the consistency of the laser penetration into the sample, and perform grains analysis to ensure the grain structure of the metals is as needed. We can also check if inclusions entered the weld and look for voids.
Laser Welding Analysis for a Titanium Pacemaker
The image on the left is of a titanium pacemaker case; the arrow shows the weld location. The image on the right is of the same object but taken with a Leica DVM6M digital microscope.
Iron/Aluminum Weld Analysis
The image on the left is of an iron/aluminum weld taken after mechanical polishing with no other post-processing. Note the laser over-penetrated the bottom substrate. The image on the right is of the same object but at 50x magnification using a Leica DM2700M microscope.
These optical microscope images at 100x magnification show details of laser penetration and material movement from one substrate to the other. These images were taken using a Leica DM2700M microscope.
These SEM images of the weld area were taken with a ThermoFisher Apreo S SEM using a backscatter detector to highlight material movement at weld locations and voids.
The EDS data to the right, captured by Oxford Instruments, Ultimax 100 EDS system, shows Iron, Carbon, and Oxygen mixing with Aluminum in the weld area.
Material Etching To Observe Grain Structure
Chemical etching with acids is the most common method of treating materials to observe grain structure for further analysis. Chemical etching is a tried and true method in metallography for over a hundred years. There are numerous reference books on how to use and mix acids. However, using acids may not be a good option for etching metals in some cases. The lab may not have access to or not be allowed to use acids or materials on the substrate observed may be heavily affected by the acids and could interfere with the observation of grain structure after etching.
Another method of etching is possible via the use of an ion mill. Ion mills typically provide an excellent finish, beyond the capabilities of mechanical polishing, before high magnification optical imaging or SEM imaging. Ion mills are normally used to provide a smooth, scratch-free surface. Ion milling also removes smear from soft materials and provides observes grain structure for Electron Backscatter Diffraction (EBSD), which even the most delicate mechanical polishing may have modified.
In this case, we used a Leica TIC3X ion mill. Typically the Leica is used with three ion sources/guns turned on to obtain a smooth surface. The sources are set up 30 degrees from each other to provide an overlapped polishing area and a very smooth polish. Unlike the regular use of the ion mill, in the case below, we purposefully used the ion mill to highlight grains for investigation. In this case, we only used one source, providing a much more directional ion beam to highlight the grain structure of the copper. As the milling rate varies depending on the direction of the grain, we can bring out the structure of the individual grains for future investigation, allowing us to avoid using acids that require specialized equipment and training.
The image on the left, taken with a Leica DM2700M microscope, is of an electronic component after final mechanical preparation using an Alumina final polish step. Notice copper grains are faintly visible. The image on the right shows the same component after etching with an ion mill; the grain structure of copper is clearly visible.
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