A materials scientist measures the shear yield stress—the minimum shear stress…
CHEMISTRY · Multi-part · AP · Chemistry · Compound Structure and Properties · Compound Structure and Properties
Problem
A materials scientist measures the shear yield stress—the minimum shear stress required for permanent (plastic) deformation—for two samples, both with identical cross-sectional area:
• Sample X: pure aluminum
• Sample Y: an aluminum–magnesium alloy containing 3 % Mg by mass (Mg atoms have slightly smaller atomic radii than Al)
The measured values are summarized in the table.
Sample
Shear yield stress / MPa
X
45
Y
62
Assume both samples have comparable grain sizes.
Use the data and particulate-level reasoning to explore how alloying influences mechanical properties.
(a) Calculate the percentage increase in shear yield stress when Mg is alloyed with Al.
(b) At the particulate level, describe how randomly distributed Mg atoms in the Al lattice can hinder dislocation movement.
(c) Explain why the data in part (a) are consistent with your description in part (b).
(d) A manufacturer wants an aluminum alloy that is even less malleable than Sample Y but must retain at least 90 % of pure aluminum’s electrical conductivity. Propose a modification to the alloy’s composition or microstructure that could meet this goal, and justify your recommendation.