According to an article published Jan. 9 in the journal Nature Communications, researchers from the University of California, Los Angeles (UCLA) employed nanotechnology to achieve a crack-free arc weld of 7075 aluminum alloy.

The research team fabricated an AA7075 filler rod with 1.7 vol-% titanium carbide (TiC) nanoparticles measuring 40 to 60 nm. They tested the new filler rod against conventional AA7075 filler and ER5356 filler during gas tungsten arc welding (GTAW) of two 3.175-mm-thick AA7075 sheets under identical parameters. The nanotreated filler yielded an even weld bead with no signs of cracking, while the conventional fillers exhibited cracks in the bead’s melting zones.

Lightweight yet strong alloys are especially critical to transportation applications. Reducing a vehicle’s weight can drastically reduce its fuel consumption as well as emissions. For this reason, automotive manufacturers have experimented with aluminum chassis components for decades. Ford’s thirteenth-generation F-series trucks, produced since 2015, replaced many steel body panels with aluminum variants and shaved an average of 600 lb off the vehicles. Widespread adoption of strong, lightweight alloys in the automotive industry is largely driven by the alloy’s weldability.

AA7075 has an excellent strength-to-weight ratio, but the alloy has long been considered unweldable due to its susceptibility to hot tearing. When used in the aerospace industry, AA7075 is typically joined using rivets or bolts, and more recently friction stir welding (FSW) has successfully welded the alloy. However, due to FSW’s difficulty with complicated welds and difficult-to-access spaces, arc welding is highly desirable for joining AA7075.

Figure 1: A comparison of the weld beads produced in the study. Conventional AA7075 and ER5356 fillers both yielded macroscopic cracks, but a nanotreated AA7075 filler rod produced an even bead with no cracks. Image source: Nature Communications / CC BY 4.0

The UCLA researchers produced arc-weld joints with a tensile strength up to 392 megapascals (Mpa). Like with other nanotechnology-based postwelding heat treatments, tensile strength increases up to 551 Mpa, 96% of the wrought material’s property, which is comparable to many steels. The researchers found that the TiC nanoparticles modified AA7075’s alpha grain and secondary phase morphologies to produce a strong, crack-free fusion joint.

The UCLA team was not the first to employ a nanoparticle-enhanced filler to solve a difficult-to-weld alloy. In a 2013 article, a University of Wisconsin research team used a filler enhanced with aluminum-oxide nanoparticles to arc-weld A206 aluminum-copper alloy, which has a susceptibility to hot tearing similar to that of AA7075. That study found that the nanoparticle filler drastically improved A206’s hot-tearing resistance, much more so than traditional grain-enhancement techniques.