AERA Materials, Coatings & Surface Finishing Flashcards

What is the Ra (average roughness) measurement scale used by AERA and what does a lower Ra value indicate about a surface?

Answer: Ra measures average peak-to-valley height in microinches or microns; lower Ra means a smoother surface

Ra quantifies surface texture by averaging the absolute deviations of the surface profile from the mean line, and a lower Ra number means fewer and shallower peaks and valleys.

Why does AERA advise against using an overly smooth (mirror-like) finish on cylinder bores for cast iron rings?

Answer: Cast iron rings require some surface texture to retain oil and seat properly; a mirror finish causes ring scuffing and oil starvation

Without micro-valleys to hold oil, a mirror-smooth bore starves the ring-to-bore interface of lubrication, leading to scuffing especially during initial break-in.

What is the purpose of phosphate coating (Parkerizing) applied to some engine components during rebuilding?

Answer: Provides corrosion resistance and a microscopic oil-retaining surface on ferrous parts

Phosphate conversion coatings create a porous iron phosphate layer that resists rust and absorbs oil, serving as a break-in lubricant carrier on parts like piston rings and camshafts.

According to AERA material guidelines, what type of bearing insert material is commonly used in high-performance rebuilt engines for superior fatigue strength?

Answer: Tri-metal bearings (steel back, copper-lead intermediate, babbitt overlay)

Tri-metal bearings offer a hard steel backing for support, a fatigue-resistant copper-lead layer, and a soft babbitt overlay that embeds debris and conforms to the journal.

What material property makes ductile iron (nodular iron) camshafts preferable over grey iron camshafts in rebuilt performance engines?

Answer: Higher tensile strength and impact resistance due to spheroidal graphite structure

The spheroidal (nodular) graphite in ductile iron interrupts crack propagation less than the flake graphite of grey iron, providing greater strength and resistance to lobe chipping under high spring loads.

Which surface treatment does AERA recognize for improving wear resistance of valve stems in rebuilt cylinder heads?

Answer: Chrome plating or stellite hardfacing on the stem and tip area

Chrome-plated or stellite-hardened valve stems resist the abrasive wear from valve guide contact and repeated seating impacts in high-mileage or high-performance applications.