Some info on M2 metal matrix tubing I found:
"Aluminum Metal-Matrix Composites
I'm sure you've heard of aluminum MMC's. Specialized has marketed its M2 line of bikes featuring Duralcan MMC tubing for several years now. The Duralcan material is an alloy of aluminum (for bike-industry purposes manufacturers use either 6061 or 7005 base material) combined with a ceramic material; in the case of the M2 it's aluminum oxide (Al2O3). Duralcan has a patented process by which it adds the Al2O3 while the aluminum is molten and in a vacuum.
The benefits of the process are apparently numerous, but for we tight-wad bikies, the big advantage is that it's a cheap way to produce this material. If aluminum oxide sounds familiar to you, it might be because you've sanded something with Al2O3 sandpaper in the past. If so, you've used essentially the same stuff that goes in these tubes: 600 grit aluminum oxide. That's right, sandpaper. Different percentages of Al2O3 yield different results. The M2 bikes have about 10 percent Al2O3 (by weight) in their mix. Which means they're 90-percent aluminum. Changing the volume fraction of the ceramic allows you to adjust the mechanical properties. Add more Al2O3 and stiffness goes up, but elongation and fracture toughness suffer. With a 10-percent mix, the material has about 8-percent higher yield strength, and 20-percent greater stiffness. The trade-off is that the elongation will be reduced, but to a claimed value of approximately 10 percent, which is acceptable.
Aluminum bikes are stiff enough, you say. True, but as you also know, this is a function of individual design. Suppose you are designing the rear end of a bike, and you want a certain level of stiffness, and you also want plenty of clearance for mud, heels, tires and chainrings. Smaller diameter tubes make it easier to accomplish this, and if you want the stiffness with smaller tubes, you benefit from having a higher modulus. With higher modulus material, you can also reduce the size of your main frame tubes so they don't resemble giant sausages.
The tangible benefit in being able to change the modulus of the different tubes for different applications is that where stiffness is more important, you can have that. Where you're more concerned about the ductility issue, as around the head tube junctions, you can enhance that property. These relatively small but important advances are great examples of what will continue to drive the evolution of bicycle frames.
Heat treatment is performed virtually the same as with a 6061 alloy. If you don't want to or can't heat treat, 7005 is also used for MMCs. Although it hasn't seen much commercial use yet, I'm sure by the time the 1995 models hit the tradeshow floors, you'll see them. The strength numbers don't really change over a standard 7005 alloy, but you can get those increases in modulus mentioned previously. "
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