• 소성∙가공
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• 제31권3호
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• pp.160-166
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• 2022

The purpose of this study is to investigate the effects of combined addition of Ca and Y on the precipitation and age-hardening behavior of an extruded AZ91 alloy by conducting the aging treatment at 200 ℃ for hot-extruded AZ91 and AZ91-0.3Ca-0.2Y alloys. In the AZ91 alloy, many Mg₁₇Al₁₂ discontinuous precipitate (DP) bands formed during air cooling immediately after extrusion are present, whereas in the AZ91-0.3Ca-0.2Y alloy, a few DP bands and numerous Al₂Y, Al₈Mn₄Y, and Al₂Ca phase particles are distributed along the extrusion direction. The peak-aging time of the AZ91-0.3Ca-0.2Y alloy is 16 hours, twice that of the AZ91 alloy. Although both alloys have similar hardness before aging treatment, the hardness after peak-aging treatment (i.e., peak hardness) of the AZ91-0.3Ca-0.2Y alloy is higher than that of the AZ91 alloy, as 93.1 and 88.7 Hv, respectively. The microstructures of both peak-aged alloys comprise DPs and continuous precipitates (CPs). However, the peak-aged AZ91-0.3Ca-0.2Y alloy has a smaller amount of DPs and a larger amount of CPs than the peak-aged AZ91 alloy. Additionally, the inter-particle spacings of DPs and CPs in the former are significantly narrower than those in the latter. These results demonstrate that the addition of small amounts of Ca and Y to a commercial AZ91 alloy considerably affects the formation rate, size, and amount of CPs and DPs during aging and resultant age-hardening behavior.

• 소성∙가공
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• 제32권4호
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• pp.173-179
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• 2023

In this study, the age-hardening behavior and tensile properties of a cast AZ91-0.3Ca-0.2Y (SEN9) alloy are investigated and compared with those of a commercial AZ91 alloy. Even after homogenization heat treatment, the SEN9 alloy contains numerous undissolved secondary phases, Al₈Mn₄Y, Al₂Y, and Al₂Ca, which results in a higher hardness value than the homogenized AZ91 alloy. Under aging condition at 200 ℃, both the AZ91 and SEN9 alloys exhibit the same peak-aging time of 8 h, but the peak hardness of the latter (86.8 Hv) is higher than that of the former (83.9 Hv). The precipitation behavior of Mg₁₇Al₁₂ phase during aging significantly differs in the two alloys. In the AZ91 alloy, the area fraction of Mg₁₇Al₁₂ discontinuous precipitates (DPs) increases up to ~50% as the aging time increases. In contrast, in the SEN9 alloy, the formation and growth of DPs during aging are substantially suppressed by the Ca- or Y-containing particles, which leads to the formation of only a small amount of DPs with an area fraction of ~4% after peak aging. Moreover, the size and interparticle spacing of Mg₁₇Al₁₂ precipitates of the peak-aged SEN9 alloy are smaller than those of the peak-aged AZ91 alloy. The homogenized AZ91 alloy exhibits a higher tensile strength than the homogenized SEN9 alloy due to the finer grains of the former. However, the peak-aged SEN9 alloy has a higher tensile elongation than the peak-aged AZ91 alloy due to the smaller amount of brittle DPs in the former.

• 동력기계공학회지
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• 제5권1호
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• pp.97-103
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• 2001

The present study was investigated changes of precipitation behaviour of laves phase in ferrite single phase and ferrite-martensite dual phase and the mechanical properties of 10%Cr ferritic alloys. In the ferrite phase, laves phase was mainly precipitated, whereas in the martensite phase, carbide was preferentially formed during the initial stage of aging and with increasing aging time. Laves phase and carbide were simultaneously precipitated by precipitation of laves phase at around carbide. Strength and toughness were lowered by the disk-type precipitator in the initial stage of aging and toughness was recovered with increasing of aging time and then, decreasing by precipitation of laves phase.

• The Journal of Asian Finance, Economics and Business
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• 제9권2호
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• pp.335-346
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• 2022

Elderly entrepreneurship is becoming increasingly important as a response to the impact of the aging population and the resulting demand on government support systems, as well as a means of ensuring long-term economic and social development. The purpose of this study is to investigate the elderly's entrepreneurial intentions in the hotel and tourism sector in Ma'anshan City, Eastern China. The researcher used an online survey of older people aged 50 to 64 in a tourism destination that is approaching an aging society stage to see if the Theory of Planned Behavior can explain the entrepreneurial ambitions of the elderly in the hospitality and tourism industry. There were 391 questionnaires gathered in all, 367 of which were valid. The data was analyzed using descriptive statistics and regression analysis. The study reveals that personal attitudes toward entrepreneurial behavior and perceived behavior control are highly influenced by societal norms. It also shows that personal attitude and perceived behavior control are antecedents of the elderly's entrepreneurial intent in this particular industry. This research adds to the research on geriatric entrepreneurship in hospitality and tourism, as well as human resource development for seniors in China, helping to alleviate the country's aging demographic concerns.

• Transactions on Electrical and Electronic Materials
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• 제15권5호
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• pp.284-289
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• 2014

The effects of additives (Nb, Bi and Cr) on the microstructure, varistor properties, and aging behavior of V/Mn/Co/ La/Dy co-doped zinc oxide ceramics were systematically investigated. An analysis of the microstructure showed that all of the ceramics that were modified with various additives were composed of zinc oxide grain as the main phase, and secondary phases such as $Zn_3(VO_4)_2$, $ZnV_2O_4$, and $DyVO_4$. The $Bi_2O_3$-modified samples exhibited the lowest density, the $Nb_2O_5$-modified sample exhibited the largest average grain size, and the $Cr_2O_3$-modified samples exhibited the highest breakdown field. All additives improved the non-ohmic coefficient (${\alpha}$) by either a small or a large margin, and in particular an $Nb_2O_5$ additive noticeably increased the non-ohmic coefficient to be as large as 36. The $Bi_2O_3$-modified samples exhibited the highest stability with variation rates for the breakdown field and for the non-ohmic coefficient (${\alpha}$) of -1.2% and -26.3%, respectively, after application of a DC accelerated aging stress of 0.85 EB/$85^{\circ}C$/24 h.

• 한국농촌간호학회지
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• 제16권2호
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• pp.37-44
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• 2021

Purpose: This study was to investigate relationships among health promotion behavior, family resilience, marital communication, and successful aging of the new middle-aged living in rural areas. Methods: Data collection was conducted from May 1 to June 20, 2021, participants were 119 adults aged 50~69 living in rural areas. The data were analyzed using the IBM SPSS/WIN 23.0 program for descriptive statistics, independent t-test, one way ANOVA, Pearson's correlation coefficient, and multiple regression. Results: As a result, factors influencing successful aging for the new middle-aged were avocation (β=-.27, p=.002.), family resilience (β=.24, p=.045), marital communication (β=.22, p=.023), gender (β=.19, p=.023), and the explanatory power of 31.0%. Conclusion: These results suggest that it is necessary to develop a program to strengthen personal avocation, family resilience, and marital communication.

• Elastomers and Composites
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• 제46권2호
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• pp.132-137
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• 2011

본 연구는 H-NBR 함량 변화에 따른 H-NBR/NBR 블렌드의 열노화 거동에 대하여 살펴보았다. 이 때 가교제로는 dicumyl peroxide와 황 혼합물을 사용하였으며, 열노화에 따른 H-NBR/NBR 블렌드의 인장강도, 파괴신율, 경도 그리고 내마모성의 변화를 살펴보았다. H-NBR을 첨가함에 따라 인장강도는 증가하였으나 내마모성은 감소하는 현상을 나타내었다. 파괴신율과 경도는 H-NBR의 영향을 받지 않았다. 노화가 진행된 모든 시편은 초기 시편보다 낮은 인장강도, 파괴신율, 경도를 나타내었다. 그러나 H-NBR의 함량이 증가함에 따라 이러한 물성저하 속도가 감소함을 알 수 있었다. 즉 H-NBR 첨가에의해 열노화 특성이 향상됨을 알 수 있었다. 모든 NBR/H-NBR 블렌드는 노화시간이 증가함에 따라 내마모성이 감소하였으며, H-NBR을 첨가한 경우 내마모성의 저하가 상대적으로 낮음을 알 수 있었다.

• 한국재료학회지
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• 제22권7호
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• pp.329-334
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• 2012

Two types of nanoclusters, termed Cluster (1) and Cluster (2) here, both play an important role in the age-hardening behavior in Al-Mg-Si alloys. Small amounts of additions of Cu and Ag affect the formation of nanoclusters. Two exothermic peaks were clearly detected in differential scanning calorimetry(DSC) curves by means of peak separation by the Gaussian method in the base, Cu-added, Ag-added and Cu-Ag-added Al-Mg-Si alloys. The formation of nanoclusters in the initial stage of natural aging was suppressed in the Ag-added and Cu-Ag-added alloys, while the formation of nanoclusters was enhanced at an aging time longer than 259.2 ks(3 days) of natural aging with the addition Cu and Ag. The formation of nanoclusters while aging at $100^{\circ}C$ was accelerated in the Cu-added, Ag-added and Cu-Ag-added alloys due to the attractive interaction between the Cu and Ag atoms and the Mg atoms. The influence of additions of Cu and Ag on the clustering behavior during low-temperature aging was well characterized based on the interaction energies among solute atoms and on vacancies derived from the first-principle calculation of the full-potential Korrinaga-Kohn-Rostoker(FPKKR)-Green function method. The effects of low Cu and Ag additions on the formation of nanoclusters were also discussed based on the age-hardening phenomena.

• 펄프종이기술
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• 제43권3호
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• pp.66-72
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• 2011

The annals of Joseon Dynasty is one of UNESCO's Memory of the World Register. For the safety preservation of the waxed annals of Joseon Dynasty, the acidic and alkaline aging mechanism of beeswax and beeswaxed Hanji has been investigated. The weight loss of beeswaxed Hanji by the acidic aging was higher than those of alkaline beeswax. The acid value and relative intensity of carbonyl groups in beeswax were slowly increased with aging time. The strength of dewaxed Hanji was decreased with aging time. The significant changes of crystallinity of dewaxed Hanji by acidic and alkaline aging were not observed.

• 소성∙가공
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• 제30권5호
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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.