Fork - Al Alloy

The schematic representation below gives an overview of the corrosion layers encountered on the object from a first visual macroscopic observation. The surface of the metal appears etched with evidence of dendritic structure present on an intermetallic corroded layer at the limits of the original surface. The surface is covered with a thin white corrosion layer which is extensive but not continuous. The surface is not smooth, especially at the front handle. At the back, close to the neck and the root of the prongs there is a thin black corrosion layer. There is pitting corrosion with white powdery corrosion around it. Finally, there is yellowish crust, possibly due to soil.

Strati. 1: CP1 on MiCorr tool is CP2 on fig. 1
Strati. 2: SV is on some case circled by CP1. On some other area SV is just a pit without corrosion around
Strati. 3: CP1 on MiCorr tool is CP4 on fig. 1 and CP2 here is CP3 on fig. 1. CP1 here has pustule shape that occur on some area around CP2 which is a crust shape. CP1 and CP2 could be the same layer composition but in an other formation state.

Analyses performed:
XRF with portable X-ray fluorescence spectrometer (NITON XL3t 950 Air GOLDD+ analyser, Thermo Fischer®). The object is an Al-Si alloy.

XRF analysis has been made on the fork before and after polishing the metal with sandpaper to reveal the metal surface. Before polishing, high percentage of silicon was detected (up 21%). After polishing, the results indicated a high amount of aluminum (92.6%) and silicon (4.6%), as well as traces of copper (0.5%), iron (0.6%), and zinc (0.2%).

No analysis was made specifically on the corrosion layers. XRF analysis before and after polishing the surface with sandpaper shows a decrease in Si element, indicating depletion of aluminium or contamination from soil.