hs08201f10 - EMSE 201 Introduction to Materials Science &...

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EMSE 201 – Introduction to Materials Science & Engineering Fall 2010 Case Western Reserve University 1 of 3 Case School of Engineering Solution to Homework #8 Explain how answers were obtained. Give appropriate units for all numerical answers. 1) (8 points) Refer to C&R Figure 11.45. Is it possible to precipitation-harden a 2014 aluminum alloy to give it the following combinations of yield strength and ductility? If so, specify the precipitation heat treatment(s). If it is not possible, then explain why. a) σ y 410 MPa, ε f 11% b) σ y 350 MPa, ε f 20% Solution a) From Figure 11.45, the following heat treatments will satisfy the indicated material property requirements: property requirement temperature, °C time, h σ y 410 MPa 149 °C 10 1.3 -10 1.6 h = 20-40 h ε f 11% 149 °C 10 1.6 h = 40 h y 410 MPa 121 °C 10 3.0 -10 3.2 h = 1000-1500 h f 11% 121 °C 10 3.5 h (0.5 pt for each row in the table) In this case, any heat treatment that will meet the strength requirement will also meet the ductility requirement. So heating for 20-40 h at 149 °C (1 pt) , or at 1000-1500 h at 121 °C (1 pt) , will achieve the required combination of yield strength and ductility. Of the two, the treatment at 149 °C is probably more practical, lasting 1-2 days compared to 40-60 days at 121 °C. b) Again from Figure 11.45, the following heat treatments will satisfy the indicated material property requirements: (0.5 pt for each row in the table, or equivalent quantitative verbal justification) In this case, no heat treatment that will meet the strength requirement will also meet the ductility requirement. Therefore the specified combination of properties cannot be achieved through
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hs08201f10 - EMSE 201 Introduction to Materials Science &...

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