• Korean Journal of Materials Research
• /
• v.7 no.8
• /
• pp.701-706
• /
• 1997

AI-2.5wt%Li 합금을 시효처리하여 시효거동과 인장성질에 미치는 $\delta$' 상의 영향을 조사하였다. $\delta$' 상의 입자 반경은 시효 시간의 1/3승에 비례하여 조대화하였다. $\delta$' 상과 기지상과의 계면에너지는 0.0073 J/$m^2$, 확산계수는 1.42$\textrm{cm}^2$/sec, 초대화 거동은 MLSW이론에 부합됨을 알 수 있었다. 미세하고 균일하게 분포한 $\delta$'상은 전반적으로 인장강도의 상승을 가져왔으며, 평형상인 $\delta$상의 석출과 이로 인한 무석출물대의 존재로 과시효시 강도가 감소하였다. 인장변형시 전위는 초전위로 아시효와 피크시효시에는 $\delta$'상을 전단하지만 과시효시에는 $\delta$'상을 전단하지 못하고 우회하여 전위루우프를 형성한다.

• Journal of Korean Society of Steel Construction
• /
• v.9 no.4 s.33
• /
• pp.515-521
• /
• 1997

The effects of heat treatment and fiber orientation on tensile strength and fatigue behavior were studied in a continuously reinforced. magnesium-based composite Following an earlier TEM investigation, specimens were thermally aged to modified the interfacial zone between the alumina fibers and the magnesium alloy matrix. From the tensile experimental results, the ultimate tensile strength of the aged specimens were lower than that of the as-fabricated due to weak fiber-matrix interfacial strength with chemical reaction during the thermal processing. The fatigue crack growth experiments were conducted with specimens having the fiber orientation normal to the crack growth direction (longitudinal) and also specimens with the fibers oriented parallel to the crack growth direction(transverse). A comparison of the fatigue crack growth behavior indicates that aged longitudinal specimens are more resistant to fatigue crack growth the as-fabricated longitudinal specimens. Conversely, as-fabricated transverse specimens are more resistant to fatigue crack growth than aged transverse specimens.

• Korean Journal of Materials Research
• /
• v.8 no.4
• /
• pp.362-367
• /
• 1998

Mg-6Zn-2Cu 및 Mg-6Zn-1.5Si(wt%)합금의 미세조직 및 석출거동을 조사하였다. 합금은 $4 x 10^{-4}$ 의 진공분위기에서 제조하였고 용체화처리는 $435^{\circ}C$에서 8시간 행하였다. Mg-6Zn합금에 1.5wt.%Si를 첨가한 합금에서는 입계 및 입내에 $10\mu\textrm{m}$-2$\mu\textrm{m}$크기의 구형의 $MgZn_{2}$와 $Mg_{2}$Si상이 존재한다. 시효경화거동은 용체화처리된 Mg-6Zn-2Cu 및 Mg-6Zn-1.5Si합금에서 조사되었다. 결정립 미세화에 의한 경도증가효과는 Mg-6Zn-2Cu합금계에서 크게 나타났으나, 시효에 의한 경도증가효과는 Mg-Zn-Si합금계에서 크게 나타났다. 시효처리 후 생성된 석출상들은 투과전자현미경 분석결과 Mg-6Zn-2Cu합금에서는$ Mg_{2}$$Zn_{3}$이었고 Mg-6Zn-1.5Si 합금에서는 $Mg_{2}$$Zn_{11}$ /이었다.

• Korean Journal of Materials Research
• /
• v.10 no.7
• /
• pp.493-498
• /
• 2000

The effects of RRA treatment on the microstructures and mechanical properties of 7050 Al alloy were investigated by differential scanning calolimetry, transmission electron microscopy, microhardness measurement and electrical conductivity. The hardness of 2nd-step aged specimen at $175^{\circ}C$ was decreased to mimimum value and increased to a peak hardness, and then re-decreased with retrogression treatment. It was found that the hardness of 2nd-step aged specimen was further increased by 3rd step aging treatment($120^{\circ}C$x24h). The initial decrease in hardness during 2nd-step aging was due to the partial dissolution of pre-existing GP zone, the major precipitation hardening phase at T6 condition. It was confirmed that the major precipitation hardening phase at 3rd-step aging was GP zone and η' phase. The electrical conductivity increased continually through 2nd-step and 3rd-step aging treatment. It was conclude that the optium 2nd-step aging condition was at $175^{\circ}C$ for 50min by considering the hardness and electrical conductivity.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.20 no.1
• /
• pp.23-29
• /
• 1984

Nowdays, the high strength aluminum alloys are broadly used for structural purpose, but the practical strengthening method by aging treatment are not much available. So that, in this study, in order to investigate the effect of aging treatment for strengthening on the fracture characteristics of the domestic high strength Al alloy (A2024BE), the variations of the aging temperature and time were taken after solution treatment. By microstructural examination, and by SEM fractographs of the fractures, the effects of aging temperature and time were investigated, considering on the fracture behaviour. The results obtained are as follows: 1) It was confirmed by microstructural investigation that the aging temperature of $190^{\circ}C$ and the aging time of 12hours were optimal to get more sound microstructure with distribution of uniform precipitation. 2) By step aging treatment, the proper aging time for obtaining the similar microstructure without any microstructural defects could be shortened in half the normal aging time. 3)By examining the SEM fractographs of the fracture surface, it was found that, regardless of the aging treatment time and temperature, all were intergranular ductile fractures, but the aging treatment at $190^{\circ}C$ for 12 hours resulted in dimple-type-transgranular and intergranular-ductile-frature.

• Korean Journal of Materials Research
• /
• v.5 no.3
• /
• pp.333-344
• /
• 1995

Cu를 함유한 2종의 저합금 고장력강(HSLA-A, HSLA-B)\ulcorner 기계적 성질에 미치는 시효처리의 영향을 조사하였다. 탄소량이 적음에도 불구하고 Cu첨가로 석출물을 생성시킴으로서 2합금 모두 $650^{\circ}C$에서 시효한 경우 양호한 강도(HSLA-A:Y.S 703Mpa, E.L 22.6% HSLA-B:Y.S 810 Mpa, E.L 23.8%)와 인성(HSLA-A:271.4J, HSLA-B:197.5J at -5$0^{\circ}C$)의 조합을 나타내었다. 50$0^{\circ}C$에서 시효할 때 가장 높은 항복 강도를 나타내나 인성은 아주 낮은 값을 나타내었다. 50$0^{\circ}C$이상 시효 온도가 증가하면 강도는 감소하고 인성은 증가하였다. HSLA-B강의 강도가 HSLA-A 강보다 높은데, \ulcorner칭 상태에서의 강도 차이는 경화능을 증가시키는 원소인 Ni, Mn, Mo, Cu의 첨가량 차이에 의한 기지 조직의 차이에 의한 것이며, 시효한 상태에서의 강도 차이는 기지 조직과 석출 강화에 기여하는 Cu량의 차이에 의한 것으로 판단된다. 시효 경화 곡선에서 $700^{\circ}C$에서의 경도 증가는 오스테나이트-페라이트 2상 영역으로부터 냉각시 생성된 “M-A constituents”에 의한 것이다. HSLA-A강과 HSLA-B강의 충격 천이 온도는 각각 -1$25^{\circ}C$와 -145$^{\circ}C$이었다.

• Korean Journal of Materials Research
• /
• v.9 no.7
• /
• pp.695-700
• /
• 1999

Effects of two-step aging treatment on the stress corrosion cracking(SCC) resistance of 7050 Al alloy were investigated by transmission electron microscopy, electrical conductivity measurement and stress corrosion facter(SCF) evaluation. It was found that η', principal hardening phase, transformed to η during over aging above maximum hardness, and SCC resistance was improved by increasing of the size and interspacing of η particles in matrix and grain boundary. The electrical conductivity increased with aging time, but SCF decreased due to the decrease of yield strength. This results mean increase of SCC resistance The optimum two-step aging condition in forged 7050 Al alloy was to be first aged at $120^{\circ}C$ for 6h and then finally aged at $175^{\circ}C$ for 12h.

• Analytical Science and Technology
• /
• v.6 no.1
• /
• pp.141-147
• /
• 1993

The behavior of reverted austenite in Fe-Ni-Mn(Ti) maraging steels has been investigated in the temperature range from $400^{\circ}C$ to $550^{\circ}C$ using TEM equipped with EDX. Four kinds of reverted austenite appeared depending on the aging temperatures and time : Widmanstatten, granular, lath-like and recrystallized austenite. The reverted austenites are enriched in Ni and Mn due to the dissolution of precipitates and redistribution of alloying elements. Widmanstatten austenite appears unformly in the lath martensite having the K-S orientation relationship with the martensite lath, while lath-like martensites showed K-S and N relations depending on the chemistry and heat treating condition. The recrystallized austenite forms at $550^{\circ}C$ after long aging times : some becomes unstable and transforms to lath martensite on cooling.

• Journal of the Microelectronics and Packaging Society
• /
• v.8 no.3
• /
• pp.37-42
• /
• 2001

The concerns of the toxicity and health hazard of lead in solders have demanded the research to find suitable lead-free solder alloys. It was discussed that effect of the intermetallic formation and structure on the reliability of solder joints. In this study, lead-free solder alloys with compositions of Sn/3.5Ag/0.75Cu, Sn/2.0Ag/0.5Cu/2.0Bi were applied to the 48 $\mu$BGA packages. Also, the lead-free solder alloys compared with eutectic Sn/37Pb solder using shear test under various aging temperature. Common $\mu$BGA with solder components was aged at $130^{\circ}C$, $150^{\circ}C$ and $170^{\circ}C$. And the each temperature applied to 300, 600 and 900 hours. The thickness of the intermetallics was measured for each condition and the activation energy for their growth was computed. The fracture surfaces were analyzed using SEM (Scanning Electron Microscope) with EDS (Energy Dispersive Spectroscopy). These results for reliability of lead-free interconnections are discussed.

• Journal of the Microelectronics and Packaging Society
• /
• v.9 no.1
• /
• pp.35-41
• /
• 2002

Flip-chip interconnection that uses solder bump is an essential technology to improve the performance of micro-electronics which require higher working speed, higher density, and smaller size. In this paper, the shear strength of Cr/Cr-Cu/Cu UBM structure of the high-melting solder bump and that of low-melting solder bump after aging is evaluated. Observe intermetallic compound and bump joint condition at the interface between solder and UBM by SEM and TEM. And analyze the shear load concentrated to bump applying finite element analysis. As a result of experiment, the maximum shear strength of Sn-97wt%Pb which was treated 900 hrs aging has been decreased as 25% and Sn-37wt%Pb sample has been decreased as 20%. By the aging process, the growth of $Cu_6/Sn_5$ and $Cu_3Sn$ is ascertained. And the tendency of crack path movement that is interior of a solder to intermetallic compound interface is found.