Surface Oxide Removal in Preparation for Controlled Liquid Metal Embrittlement

During liquid metal embrittlement a liquid metal infiltrates grain boundaries of a compatible solid metal, interrupting the inter-grain bonds and weakening the metal. Ongoing research has proposed that this effect may be used to perform additive/subtractive hybrid machining to fabricate replacement components, using relatively simple equipment and low material and instrument costs. The gallium/aluminum pairing is of particular interest due to the usage of aluminum in a wide variety of structural and aerospace applications coupled with gallium's nontoxicity and melting point just above room temperature, which facilitates storage and transport. To activate aluminum to gallium infiltration, the surface oxide formed on aluminum in atmosphere must first be removed simultaneously with a significant amount of bulk metal to promote flow control of the liquid metal. Three targeted techniques for oxide removal were tested and compared, specifically mechanical abrasion, chemical etching, and laser ablation. Mechanical abrasion is simple to implement but lower precision. Chemical etching requires significant prep work and cleanup but could operate on entire sheets of substrate simultaneously with proper masking. Although laser ablation requires the most complex instrumentation, it requires minimal prep work and provides the greatest precision, making it ideal for the manufacturing application under development here.