• Title/Summary/Keyword: Aging Hardening Effect

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Effect of Pre-Aging Conditions on Bake-Hardening Response of Al-0.4 wt%Mg-1.2 wt%Si-0.1 wt%Mn Alloy Sheets

  • Lee, Kwang-jin;Woo, Kee-do
    • Korean Journal of Metals and Materials
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    • v.49 no.6
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    • pp.448-453
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    • 2011
  • Pre-aging heat treatment after solution heat treatment (SHT) of Al-0.4 wt%Mg-1.2 wt%Si-0.1 wt%Mn alloy sheets for auto-bodies was carried out to investigate the effect of pre-aging and its conditions on the bake-hardening response. Mechanical properties were evaluated by a tensile and Vickers hardness test. Microstructural observation was also performed using a transmission electron microscope (TEM). It was revealed that pre-aging treatments play a great role in the bake-hardening response. In addition, it was found that the sphere-shaped nanosized clusters that can directly transit to the needle-shaped ${\beta}$" phase during the paint-bake process, not being dissolved into the matrix, are formed at 343 K. The result, reveals that the dominant factor of the bake-hardening response is the pre-aging temperature rather than the pre-aging time.

The Effect of Ausforming Process on Mechanical Properties of Ultrahigh Strength Secondary Hardening Martensitic Steels (극초고강도 이차경화형 마르텐사이트강의 기계적성질에 미치는 오스포밍 공정의 영향)

  • Kim, S.B.;Won, Y.J.;Song, Y.B.;Cho, K.S.
    • Journal of the Korean Society for Heat Treatment
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    • v.34 no.4
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    • pp.179-184
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    • 2021
  • Two types of secondary hardening martensitic steels, 10Co-14Ni and 6Co-5Ni, were produced by vacuum induction melting to investigate the effect of ausforming process on mechanical properties. According to the results of present study, the alloy samples ausformed at low temperature indicated a rather low hardness level in overall aging time despite the refinement of martensite lath width. As the result can closely be related with the presence of primary carbides precipitated within the initial austenite matrix, we confirmed that, in ultrahigh strength secondary hardening martensitic alloy steels, the ausforming process can rather limit the degree of secondary hardening during the subsequent aging treatment.

Effect of Fine Copper Sulfides on the High Cycle Fatigue Properties of Bake Hardening Steels for Automotive (자동차용 소부경화형(BH) 강의 고주기 피로 특성에 미치는 미세 황화물의 영향)

  • Kang, Seonggeu;Kim, Jinyong;Choi, Ildong;Lee, Sungbok;Hong, Moonhi
    • Korean Journal of Metals and Materials
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    • v.49 no.3
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    • pp.203-210
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    • 2011
  • Bake hardening steels have to resist strain aging to prevent the yield strength increment and stretcher strain during press process and to enhance the bake hardenability during baking process after painting. The bake hardening steels need to control the solute carbon and the solute nitrogen to improve the bake hardenability. Ti and/or Nb alloying for nitride and carbide precipitation and low carbon content below 0.003% are used to solve strain aging and formability problem for automotive materials. However, in the present study, the effect of micro-precipitation of copper sulfide on the bake hardenability and fatigue properties of extremely low carbon steel has been investigated. The bake hardenability of Cu-alloyed bake hardening (Cu-BH) steel was slightly higher (5 MPa) than that of Nb-alloyed bake hardening (Nb-BH) steel, but the fatigue limit of Cu-BH steel was far higher (45 MPa) than that of Nb-BH steel. All samples showed the ductile fracture behavior and some samples revealed distinct fatigue stages, such as crack initiation, stable crack growth and unstable crack growth.

Effects of Dislocation Distribution and Carbon Effective Diffusion on Strain Aging Behavior of a Low Carbon Dual Phase Steel (저탄소 Dual Phase강의 가공시효에 미치는 탄소유효확산 및 전위분포의 영향)

  • Yoo, S.H.;Jung, K.C.;Hong, K.H.;Park, KT.
    • Transactions of Materials Processing
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    • v.30 no.5
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    • pp.226-235
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    • 2021
  • The strain aging behavior of a low carbon dual phase steel was examined in two conditions: representing room temperature strain aging (100 ℃ × 1 hr after 7.5 % prestrain) and bake hardening process (170 ℃ × 20 min after 2 % prestrain), basing on carbon effective diffusion and dislocation distribution. The first principle calculations revealed that (Mn or Cr)-vacancy-C complexes exhibit the strongest attractive interaction compared to other complexes, therefore, act as strong trapping sites for carbon. For room temperature strain aging condition, the carbon effective diffusion distance is smaller than the dislocation distance in the high dislocation density region near ferrite/martensite interfaces as well as ferrite interior considering the carbon trapping effect of the (Mn or Cr)-vacancy-C complexes, implying ineffective Cottrell atmosphere formation. Under bake hardening condition, the carbon effective diffusion distance is larger compared to the dislocation distance in both regions. Therefore, formation of the Cottrell atmosphere is relatively easy resulting in to a relatively large increase in yield strength under bake hardening condition.

Effect Of The Microstructure And Aging Treatment Conditions On Strength Of High Strength Invar Alloy (고강도 인바합금의 강도에 미치는 미세구조와 시효처리 조건의 영향)

  • Jung, J.Y.;Lee, K.D.;Ha, T.K.;Jeong, H.T.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2007.10a
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    • pp.322-325
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    • 2007
  • Precipitation characteristics of the Fe-36Ni based high strength Invar alloy for power transmission wire was investigated in this study. High strength can be obtained in this alloy through solution hardening, precipitation hardening and strain hardening by cold working. In the present study, ingots of Fe-36Ni based Invar alloys with the contents of C, Mo and V varied. Microstructure observations by OM, SEM, and TEM were carried out to validate the simulation results. BCC phase and $FeNi_3$ phase are also expected at lower temperatures below $500^{\circ}C$. Aging treatments were carried out at temperatures ranging from 400 to $900^{\circ}C$ for time intervals from 3 min to 100hrs. Peak aging condition was obtained as $400^{\circ}C$ and 1 hr. With temperature increased, peak strength was decreased abruptly. Microstructure observation was conducted by optical microscopy, scanning electron microscopy, and transmission electron microscopy.

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Effect of Strain Aging on Tensile Behavior and Properties of API X60, X70, and X80 Pipeline Steels

  • Lee, Sang-In;Lee, Seung-Yong;Lee, Seok Gyu;Jung, Hwan Gyo;Hwang, Byoungchul
    • Metals and materials international
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    • v.24 no.6
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    • pp.1221-1231
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    • 2018
  • The effect of strain aging on tensile behavior and properties of API X60, X70, and X80 pipeline steels was investigated in this study. The API X60, X70, and X80 pipeline steels were fabricated by varying alloying elements and thermomechanical processing conditions. Although all the steels exhibited complex microstructure consisting of polygonal ferrite (PF), acicular ferrite, granular bainite (GB), bainitic ferrite (BF), and secondary phases, they had different fractions of microstructures depending on the alloying elements and thermomechanical processing conditions. The tensile test results revealed that yielding behavior steadily changed from continuous-type to discontinuous-type as aging temperature increases after 1% pre-strain. After pre-strain and thermal aging treatment in all the steels, the yield and tensile strengths, and yield ratio were increased, while the uniform elongation and work hardening exponent were decreased. In the case of the X80 steel, particularly, the decrease in uniform elongation was relatively small due to many mobile dislocations in PF, and the increase in yield ratio was the lowest because a large amount of harder microstructures such as GB, BF, and coarse secondary phases effectively enhanced work hardening.

A Study on the Development for the Vehicle Engine Mountion Bracket Using Squeeze Casting (스퀴즈 캐스팅 제조법에 의한 자동차 엔진 마운틴 브래킷 개발에 관한 연구)

  • Kim, S.H.
    • Journal of Power System Engineering
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    • v.7 no.4
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    • pp.44-48
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    • 2003
  • Alumium alloys casting are gaining increased acceptance in the automotive and electronic industeries and squeeze casting is the most efficient method of manufacturing such mass produced parts. This study has been investigated the microstructures and mechanical properties of Al-7.0Si-0.4Mg(AC4C)alloy fabricated by squeeze casting process for development of Engine Mountain Bracket. The microstructure of squeeze casted specimen were composed of eutectic structure Alumimim solid solution and $Mg_2Si$ precipitates. The tensile strength of as-solid solution treatment Al-7.0Si-0.4Mg alloy revealed 2985MPa. It was found that Al-7.0Si-0.4Mg alloy have good aging hardening effect results are presented to show the validity of the control method.

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Effect of Aging Treatment on the Microstructures and Mechanical Properties of 7N01 Aluminium Alloy (7N01 Al 합금의 미세조직 및 기계적 성질에 미치는 시효처리의 영향)

  • Hwang, Youn-Gu;Kang, Min-Chul;Kang, Jung-Youn;Kim, In-Bae
    • Journal of the Korean Society for Heat Treatment
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    • v.13 no.2
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    • pp.103-107
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    • 2000
  • Effect of aging treatment on the microstructures and mechanical properties of 7N01 Al alloy was investigated by differential scanning calorimetry, transmission electron microscopy, microhardness measurement and tensile test. Maximum hardness(125.7Hv) and tensile strength(447.3MPa) were obtained from the specimen aged at $120^{\circ}C$ for 32hrs. The major precipitation hardening phase was confirmed as coherent $MgZn_2({\eta}^{\prime})$ phase. Microhardness changes after peakaged condition showed very large decrease upon increased aging time. This result was attributed to the high transformation rate from coherent ${\eta}^{\prime}$ to incoherent ${\eta}$. It was found that the precipitation sequence of 7N01 Al alloy was GP zone${\rightarrow}$metastable spherical hcp $MgZn_2({\eta}^{\prime}){\rightarrow}$ equilibrium rodlike hcp $MgZn_2({\eta})$.

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Effect of CaO Addition on Age Hardening Behavior of AZ91 Alloy (AZ91 합금의 시효경화 거동에 미치는 CaO 첨가의 영향)

  • Jun, Joong-Hwan
    • Journal of the Korean Society for Heat Treatment
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    • v.24 no.4
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    • pp.193-198
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    • 2011
  • Effect of CaO addition on age hardening response has been studied by using optical microscopy, scanning electron microscopy and differential thermal analysis in AZ91 and CaO-containing ECO-AZ91 alloys. After solution treatment, the ${\beta}$($Mg_{17}Al_{12}$) phase formed during solidification mostly disappeared in the microstructure in the AZ91 alloy, whereas numerous ${\beta}$ precipitates containing Ca were still observed in the ECO-AZ91 alloy due to its enhanced thermal stability. The ECO-AZ91 alloy showed the delayed peak aging time and higher peak hardness compared with those of the AZ91 alloy. The activation energies for ${\beta}$ precipitation calculated by means of Kissinger method increased from 71.4 to 85.6 kJ/mole by the addition of CaO, which implies that CaO plays a role in reducing ${\beta}$ precipitation rate in the AZ91 alloy.

Fabrication of AC4A/$SiC_w$composite by squeeze casting(II) (용탕단조법에 의한 AC4A/$SiC_w$복합재교 제조에 관한 연구(ll)-가압력 및 시효특성-)

  • Mun, Gyeong-Cheol;Lee, Chun-Hui
    • Korean Journal of Materials Research
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    • v.3 no.6
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    • pp.606-613
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    • 1993
  • This was studied about aging characteristic of AC4A/$SiC_{w}$ 10-30v/o reinforced composite. Aging hardenability was decreased $SiC_{w}$ 30% > 10% > 20%. Aging hardening of T6 treatmented composite was higher absolute value than AC4A I/M material. And this results indicated initial hardening phenomenon according to increase $SiC_{w}$ volume fraction. Reinforced effect by pressure was the same effect as before aging treatment and the best condition pressure at 75MPa. Similar to reinforced effect according to $SiC_{w}$ volume fraction was 30 % > 10 % > 20 %. In case of pressure is low, whisker is not break the same time press with base metal after wetting. After it is wetting with base metal, a part transformed or wetting part break and whisker maintain original shape or a part transformed on the otherhand, in case of pressure is high, whisker is break in same time it was not against pressure and whisker's shape is near a polygon or spherical shape.

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