Transcript Masters_Project_Final_Report.pptx

Evaluation of Coating Methods for Corrosion
Protection of Magnesium Castings
RPI Masters Project Final Report
Siobhan Fleming
8/6/12
Agenda
 Project Review
 Research Review
 Magnesium
 Magnesium Alloys
 Magnesium Coatings
 Recommendations for alloys and coatings
Project Review
 Extensive review of technical journals completed
 Magnesium Alloys
 Coating for corrosion protection
 Review highlighted new technology in coatings that may be
very successful in corrosion protection with more research.
 Good alloys for certain application were identified
throughout the document and segregated in a final table.
Research Review
 Technical journals reviewed through electronic village
 Offered excellent details for specific uses
 Provided insight into new technologies
 Specific texts reviewed for background on magnesium,
magnesium alloys and coatings for corrosion protection
Magnesium
 Lightest of light metal alloys
 Low Density
 Good Heat Dissipation
 Good Damping
 Good Electro-magnetic shield
 Useful in applications were weight is a critical design element
 Susceptible to corrosion
Magnesium Alloys
 Alloys designed to improve corrosion resistance
 Specific elements offer different benefits when combined
into alloy form
 Benefits are laid out in table format by element in the paper
 Each alloy has its own benefits
 Selected alloys are documented in paper for benefits
Magnesium Coatings
 Numerous different coatings provide coating protection
 Example of coating protection for aerospace applications is
provided in paper
 Cold spray appears to be the future of coatings
 More research is required on specific alloys in order to
eliminate the concern of galvanic corrosion.
Recommendations for Alloys
Alloy
Application
AZ91
Cast
Notes
Helicopter
Transmission Less costly, good tensile strength,
Housings
very susceptible to creep above
120ºC. Good corrosion resistance.
AM60/AM50/AM20
Automotive (wheels, seat frames, Greater
steering wheels)
AS41
Automotive
Aerospace
and
(crank
(landing
case, Easier than AS21 to cast with better
fluidity
wheels, Superior
tensile
gearbox housings, helicopter rotor Expensive due to silver
fittings)
fracture
toughness.
transmission housing)
QE22
ductility
properties,
Coatings Advantages and Disadvantages
Coating Type
Advantages
Disadvantages
Chemical Conversion
Most effective and mature process
Cr6+ in chromate bath is a highly toxic carcinogen
facing restrictions with use.
Phosphate Treatments
Chromate Free
Coarse grains can cause cracks; heavy metal ions
in solution can cause environmental pollution.
Anodizing
Can improve paint adhesion to metals,
Coatings are brittle and prone to cracking or
shedding after collision.
Plating (electro and electroless)
Can improve corrosion resistance depending on
Plating films have a weak adhesion to magnesium
what material is plated on surface.
alloys. Issues with galvanic corrosion depending
on type of metal used.
Sol-Gel
Can achieve better layering than electroless
Potential issues with galvanic corrosion depending
plating. Some testing has proved very successful
on material used.
using TiO2
TAGNITE
Chromate free, better abrasion resistance, wet paint
Has not been proven as a complete protection.
adhesion, impact resistance and fatigue properties.
Useful more in touch up conditions where fine
tolerances are required.
Paint
Provides a final protective coating when used in
Only provides additional protection when built up
combination of other coating techniques.
correctly with other coatings. Does not provide
protection when chipped or cracked.
Cold Spray
Adheres well with fewer issues than plasma spray.
Still a new technology, not widely tested.
Testing has proved improved corrosion resistance
Concerns with galvanic corrosion depending on
when high purity aluminum is used as sprayed
coating material used.
material.