Lightweight metals are used in a wide variety of applications due to their low density, high strength-to-weight ratio, and excellent corrosion resistance.
Various grades of aluminum (Al) and magnesium (Mg) alloys, each with distinct compositions and characteristics, are used across sectors such as aerospace, automotive, construction, packaging, and electronics.
Recycling scrap metal is a highly efficient and eco-friendly source of aluminum for these applications. Compared with primary production, the recycling process cuts greenhouse gas emissions and saves up to 95 % of the energy needed to manufacture aluminum from raw materials.
Handheld XRF (HHXRF) is a well-established instrument for scrap metal sorting. While they can identify most grades of stainless steel, as well as titanium (Ti), nickel (Ni), cobalt (Co), and copper (Cu) alloys within one to two seconds, sorting aluminum alloys can take much longer.
This is particularly true for alloys that cannot be specifically determined by their transition metal content, such as manganese (Mn), copper (Cu), zinc (Zn), nickel (Ni), iron (Fe), chromium (Cr), or titanium.
The grade separation within the AA 1000, AA 5000, and AA 6000 series, along with the casting alloy family grade separation, necessitates measurement of light elements such as magnesium and silicon (Si). To measure these elements, an X-ray beam at a lower voltage is typically used, resulting in measurements of 10 seconds or more.
Approximately 10 years ago, handheld laser-induced breakdown spectroscopy (LIBS) was introduced as an alternative for sorting aluminum and magnesium alloy grades in just a few seconds. These include a smaller spot size and fluctuations related to the transient nature of the laser-induced plasma.
In contrast to the wider, continuous X-ray beam, LIBS evaluation exhibits a higher sensitivity to surface roughness and surface contamination and is therefore less accurate than HHXRF.
Identification of aluminum alloy grades within seconds using the Thermo Scientific Niton XL5 Plus handheld XRF analyzer. Image Credit: Thermo Fisher Scientific – Handheld Elemental & Radiation Detection
More recently, the Light Metal Quick Sort (LMQS) mode available on the Thermo Scientific™ Niton™ XL5 series of handheld XRF analyzers leverages a different approach to traditional HHXRF instruments. Equipped with a 5 W (up to 500 μA) tube and an advanced silicon drift detector (SDD) with a graphene window, the analyzer begins measuring elements ranging from magnesium to zinc at low voltage.
This facilitates the identification of most aluminum and magnesium alloy grades and other alloy families within one to three seconds. Longer measurements can be configured for the few aluminum alloy grades that are identified based on zirconium (Zr), tin (Sn), lead (Pb), or bismuth (Bi) contents.
As illustrated in Figure 1, the LMQS mode is highly effective for rapidly sorting aluminum alloy grades that contain comparable transition element concentrations, but differ in light element content, such as:
- Casting aluminum alloys containing high silicon levels from wrought alloy grades
- Twin alloys that differ solely by magnesium content, such as AA3003 and AA3004, or AA2014 and AA2024 grades
- Alloys that differ by only a few tenths of a percent in silicon and magnesium content, AA1100, AA6061, and AA6063
Summary
The LMQS mode is available on some Niton analyzer models and allows recyclers processing large volumes of lightweight metals, such as larger scrap yards, aircraft dismantlers, and foundries, to maximize productivity through the quick and accurate identification of magnesium and aluminum alloy grades within just a few seconds.
This information has been sourced, reviewed and adapted from materials provided by Thermo Fisher Scientific – Handheld Elemental & Radiation Detection.
For more information on this source, please visit Thermo Fisher Scientific – Handheld Elemental & Radiation Detection.