1. RPI Masters Project Final Report Siobhan Fleming 8/6/12 Evaluation of Coating Methods for Corrosion Protection of Magnesium Castings

2. Agenda Project Review Research Review Magnesium Magnesium Alloys Magnesium Coatings Recommendations for alloys and coatings

3. 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.

4. 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

5. 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

6. 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

7. 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.

8. Recommendations for Alloys AlloyApplicationNotes AZ91 Cast Helicopter Transmission Housings Less costly, good tensile strength, very susceptible to creep above 120ºC. Good corrosion resistance. AM60/AM50/AM20 Automotive (wheels, seat frames, steering wheels) Greater ductility and fracture toughness. AS41 Automotive (crank case, transmission housing) Easier than AS21 to cast with better fluidity QE22Aerospace (landing wheels, gearbox housings, helicopter rotor fittings) Superior tensile properties, Expensive due to silver

9. Coatings Advantages and Disadvantages Coating TypeAdvantagesDisadvantages Chemical ConversionMost effective and mature process Cr 6+ in chromate bath is a highly toxic carcinogen facing restrictions with use. Phosphate TreatmentsChromate Free Coarse grains can cause cracks; heavy metal ions in solution can cause environmental pollution. AnodizingCan 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 what material is plated on surface. Plating films have a weak adhesion to magnesium alloys. Issues with galvanic corrosion depending on type of metal used. Sol-Gel Can achieve better layering than electroless plating. Some testing has proved very successful using TiO 2 Potential issues with galvanic corrosion depending on material used. TAGNITE Chromate free, better abrasion resistance, wet paint adhesion, impact resistance and fatigue properties. Has not been proven as a complete protection. Useful more in touch up conditions where fine tolerances are required. Paint Provides a final protective coating when used in combination of other coating techniques. Only provides additional protection when built up correctly with other coatings. Does not provide protection when chipped or cracked. Cold SprayAdheres well with fewer issues than plasma spray. Testing has proved improved corrosion resistance when high purity aluminum is used as sprayed material. Still a new technology, not widely tested. Concerns with galvanic corrosion depending on coating material used.