What are the advantages in using magnesium alloy instead of aluminum a
What are the advantages in using magnesium alloy instead of aluminum a
(OP)
I've started doing vibration fixtures for electronic equipment. I learned that many people are using Magnesium alloy instead of aluminum. Can anybody tell me what are the advantages in using magnesium?
Thank in advance for your insight!
Thank in advance for your insight!





RE: What are the advantages in using magnesium alloy instead of aluminum a
RE: What are the advantages in using magnesium alloy instead of aluminum a
For beam stiffness and minimum, the defining relationship which dictates the optima is (E^0.5 / rho).
Material E (GPa) rho(Mg/m^3) ratio
Steel 200 7.85 1.8
Aluminum 70 2.8 3.0
Magnesium 41 1.75 3.7
So for the same mass, aluminum in bending can be as high as 1.7 times (3.0/1.8) stiffer than steel, but magnesium can be more than 2x (3.7/1.8) times stiffer than steel.
Hopefully this post makes sense.
Brad
RE: What are the advantages in using magnesium alloy instead of aluminum a
Cheers
Greg Locock
RE: What are the advantages in using magnesium alloy instead of aluminum a
Regarding the specific stiffness (E/density) I think it depends very much on which alloys you pick. If you look at this link, for example, the specific stiffnesses for a particular pair of aluminum and magnesium alloys are virtually identical - or at least very much closer than you are claiming. Unless of course the link is incorrect, which wouldn't surprise me. (It's Chinese).
http://www.wahhong.com.tw/engpage/m3.htm
RE: What are the advantages in using magnesium alloy instead of aluminum a
Magnesium transmission casings
Thread78-41560
RE: What are the advantages in using magnesium alloy instead of aluminum a
RE: What are the advantages in using magnesium alloy instead of aluminum a
I do think it is should be pointed out that if you have, say, a cantilever beam which is required to be equally stiff in all directions, then there is no advantage in using magnesium from the point of view of natural frequency - because in that case the natural frequency is simply proportional to the square root of specific stiffness, or (E/rho)^0.5 , and magnesium is then actually the worst of all using your figures. It is only when you are interested in preferentially stiffening the beam in one direction that you get the E^0.5/rho relationship.
RE: What are the advantages in using magnesium alloy instead of aluminum a
CurlyJon
RE: What are the advantages in using magnesium alloy instead of aluminum a
Can i just ask one question? In the case of most efficient vibration transmitter, does it follow that aluminium alloy would be the best material to use since it has low material damping?
Thanks,
regards,
RE: What are the advantages in using magnesium alloy instead of aluminum a
CurlyJon
RE: What are the advantages in using magnesium alloy instead of aluminum a
But this is not the issue in fixture design, because you are attaching (for the fixture) a lumped mass. In this case, it is mainly the E that will contribute to the stiffness. So in that sense, steel would be the choice. Due to weight limitations of the shakers this is not always possible, and hence a lower density material is used. In order for a Al fixture with a mass attached to it to have the same natural frequency as a steel fixture, the geometry neeeds to be altered. (Cross sections/Area moments of Inertia) So the same goes for Mg. Even lower E requires even higher geometrical stiffness for the same natural frequency as the steel fixture with the same mass attached.
If the design is clever, mass of a Al or Mg fixture will be lower than the steel.
I think the material damping in Al or (even higher in) Mg will have a small influence. The alloying components will tend to reduce the initially good damping properties of pure Al or Mg.
Bernt
RE: What are the advantages in using magnesium alloy instead of aluminum a
Sorry I didn't reply earlier (very little surfing lately).
Again, my source is M. Ashby for the values stated (I apologize for lack of citation). Ashby's text is a highly-respected text for materials in design (and he's British, so he must be right
Specific stiffness of most structural metals ("area") is pretty close, which is why steel is usually used for axial/pure shear loads (it's cheap and just as good).
Regarding your last post: my stated relationship holds whether it is one direction or both directions of a cantilever, presuming one can use a "box" section (I think your statement is presuming a solid section, and I will agree with you that there is no benefit under that scenario).
Cheers,
Brad
RE: What are the advantages in using magnesium alloy instead of aluminum a
RE: What are the advantages in using magnesium alloy instead of aluminum a
My idea was poorly communicated in my last post. You are correct--for unidirectional cantilever loading, the relationship holds whether a solid section or box/pipe section. For bi-directional cantilever loading, a "hollow" section must be utilized to benefit.
The formal citation: Michael F. Ashby, "Materials Selection in Mechanical Design". He describes the means to derive this (and gives great charts on these relationships). I will work to derive and post this in a coherent manner; it's been a few years since I did the derivation.
I'll endeavor to post this in the next few days.
Cheers,
Brad
RE: What are the advantages in using magnesium alloy instead of aluminum a