Light Alloys Flashcards
How does magnesiums density compare with other structural metals?
the most outstanding characteristics of magnesium (Mg) is its density, 1.74 gcm-3. this is the lowest of akllk the structural metals, (lithium is the lowest of all metals.
How can the high temperature strength of magnesium be increased?
High temperature strength in Mg alloys can be inporved by the use of ceramic particles or fibres, eg SiC to produce metal - metric - composites (MMC). the solubility of many elemetns, in magnesium, increases with temperature (e.g. Al in Mg), therefore dispersion strengthening is possible.
what is plastic deformation occuring within an alloy?
Plastic deformation is the resukt of slip occuring in the metal. slip is the movement of one part of the creystal relative to another. slip always occurs on the same crystallographic planes. the deformation is permanent.
what is the critical shear stress and for different slip systems how can it be altered?
CRSS: the stress required to initiate slip in a pure single crystal. on increase of temperature the value decreases.
what are the two types of deformation? what are the differences between them?
Slip plane and twinning deformation. slip plane includes deformation greater than the atomic spacing, whereas, twinning can include deformation less than the atomic spacings. the orientation of the atoms remain the same for slip plane whereas twinning results in a change in orientation.
hat is the effect known as hot tearing? where does it occur and how? what effect does it have on a cast alloy?
hot tearing is a common casting default occuring involving the formation of a crack within a cast part. it occurs within the mushy zone of an alloy due to the miss match between the reate of shrinkage of the alloy on solidification and the compensation by additional liquid. it causes breakages within the cast piece.
