Aluminum Joining Intensifies
The use of aluminum in cars is expected
to nearly double by 2025, and today it’s
already the second-most-used material
to produce cars. Manufacturers have had
to develop new joining and assembly
methods to meet the demand for alumi-num-intensive vehicles (AIVs). Alcoa
951 by Alcoa Inc. is one of these new
technologies. A pretreatment bonding
material that significantly strengthens
adhesive bonds between aluminum substrates, Alcoa 951 creates a highly durable bond that is nine times more durable
than titanium-zirconium applications.
The surface treatment is applied through an immersion or spray application in
which its organic components bond with oxides present on the metal surface.
The molecular structure chemically binds aluminum oxide with one end and
adhesive with the other end. This creates a strong link at the molecular level,
resulting in lasting, durable joints for automotive structures. The minimal level
of treatment on the surface makes it ultra-thin and essentially transparent to
downstream processes such as forming, resistance spot welding and painting.
Alcoa 951 has already been integrated into automotive assembly and is used to
build the 2015 Ford F150 truck.
◗ Alcoa Inc., www.alcoa.com
Corrosion Prevention Goes Green
The replacement of hazardous hexavalent chromium compounds in structural adhesive bond primers has been a problem for the aerospace industry.
Because they’re extremely vulnerable to localized
corrosion, aluminum structures must be bonded with high-performance materials. The highly
toxic strontium-chromate additive is currently
used to meet stringent safety standards, despite its
heavy regulation throughout the world. But now
there’s an effective alternative: Eco Tuff. Developed
by United Technologies Research Center, and
licensed and sold through Pratt & Whitney, Eco-Tuff is a multi-mode, non-chromated corrosion
inhibitor for aluminum alloys. This pigment additive contains three agents that act synergistically
to inhibit the localized corrosion of aluminum
alloys. A molybdate-oxyanion complex acts as an anodic corrosion inhibitor
and a cerous ion is added as a cathodic corrosion inhibitor. The cerous ion is
tightly bound to a citric acid molecule by three covalent bonds. This structure,
a chelated cerium citrate complex, lets the inhibitors do their work without
risks of unwanted reactions between them. Eco Tuff has been licensed to 3M
Company, and is now used as the active corrosion-inhibiting ingredient in 3M’s
EW-5000ET aerospace adhesive bond primer.
◗ United Technologies Research Center, www.utrc.utc.com
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