신소재개론 및 설계 (기초 2) ISSUES TO ADDRESS... • How are metal alloys classified and how are they used? • What are some of the common fabrication techniques? 1

금속의 분류 Steels Cast Irons <1.4wt%C 3-4.5 wt%C Eutectic: Eutectoid: Fe 3 C cementite Metal(금속) Steels Ferrous(철) Nonferrous(비철) Cast Irons Cu Al Mg Ti <1.4wt%C 3-4.5 wt%C Steels Cast Irons <1.4wt%C 3-4.5 wt%C T(°C) 1600 d L 1400 g +L 1200 g L+Fe 3 C 1148°C austenite Eutectic: 1000 4.30 a g +Fe 3 C + a 800 g 727°C ferrite Eutectoid: 6 00 0.77 a +Fe 3 C 4 00 1 2 3 4 5 6 6.7 (Fe) C 2 o , wt% C

강(STEELS) 3

비철 합금 NonFerrous Alloys • Cu Alloys • Al Alloys • Mg Alloys B rass : Zn is subst. impurity (costume jewelry, coins, corrosion resistant) Bronze : Sn, Al, Si, Ni are subst. impurity (bushings, landing gear) Cu-Be : precip. hardened for strength • Al Alloys -lower r : 2.7g/cm 3 -Cu, Mg, Si, Mn, Zn additions -solid sol. or precip. strengthened (struct. aircraft parts & packaging) • Mg Alloys -very low : 1.7g/cm -ignites easily - aircraft, missles • Refractory metals -high melting T -Nb, Mo, W, Ta • Noble metals -Ag, Au, Pt oxid./corr. resistant • Ti Alloys : 4.5g/cm vs 7.9 for steel -reactive at high T space applic. 4

금속의 제조(제철) 5

금속의 가공(포밍) FORMING • Forging (wrenches, crankshafts) • Rolling (I-beams, rails) often at elev. T • Drawing (rods, wire, tubing) • Extrusion (rods, tubing) 6

금속의 가공(주조) CASTING • Sand Casting • Die Casting (large parts, e.g., auto engine blocks) • Die Casting (high volume, low T alloys) • Continuous Casting (simple slab shapes) • Investment Casting (low volume, complex shapes e.g., jewelry, turbine blades) plaster die formed around wax prototype 8

금속의 가공(용접) JOINING • Powder Processing • Welding (materials w/low ductility) • Welding (when one large part is impractical) • Heat affected zone: (region in which the microstructure has been changed). 9