Thermal Parameters And Microstructural Development In Directionally Solidified Zn-rich Zn-mg Alloys

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Transient directional solidification experiments have been carried out with Zn-Mg hypoeutectic alloys under an extensive range of cooling rates with a view to analyzing the evolution of microstructure. It is shown that the microstructure is formed by a Zn-rich matrix of different morphologies and competitive eutectic mixtures (Zn-Zn11Mg2 and Zn-Zn2Mg). For 0.3 wt-pct Mg and 0.5 wt-pct Mg alloys, the Zn-rich matrix is shown to be characterized by high-cooling rates plate-like cells (cooling rates > 9.5 and 24 K/s, respectively), followed by a granular-dendritic morphological transition for lower cooling rates. In contrast, a directionally solidified Zn1.2 wt-pct Mg alloy casting is shown to have the Zn-rich matrix formed only by dendritic equiaxed grains. Experimental growth laws are proposed relating the plate-like cellular interphase, the secondary dendritic arm spacing, and the eutectic interphase spacings to solidification thermal parameters, i.e., cooling rate and growth rate. The experimental law for the growth of secondary dendritic spacings under unsteady-state solidifications is also shown to encompass results of hypoeutectic Zn-Mg alloys subjected to steady-state Bridgman growth.47A630523064FAPESP-Sao Paulo Research Foundation, Brazil [2012/08494-0, 2013/15478-3, 2013/25452-1, 2013/23396-7, 2014/50502-5]CNPq-The Brazilian Research CouncilCSIC-Spanish National Research Council [i-link0944]Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Interrelationship of thermal parameters, microstructure and microhardness of directionally solidified Bi–Zn solder alloys

Due to the health and environmental concerns associated with lead usage, the research on alternative lead-free alloys for replacing lead-based solders is a global demand. Despite numerous studies on Sn-based lead-free solders in recent years, there is not yet a standard solder alloy able to cover the spectrum of properties furnished by the classic Sn-Pb alloy. In this sense, particular lead-free alloys compositions have been suited for specific needs and the options have been broadening when elements other than tin are used as the base component, such as indium, gold and bismuth. The later element is well known in the hall of lead-free alloys as an alloying option rather than as a base component. This study aims to establish interrelations of solidification thermal parameters (growth and cooling rates), microstructure features (primary and secondary dendrite arm spacings – λ1 and λ2; eutectic spacing – λE and interphase spacing – λint) and hardness of Bi-Zn alloys (1.5 wt% Zn-hypoeutectic, 2.7 wt% Zn-eutectic, and 5 wt% Zn-hypereutectic alloys) samples, which were directionally solidified in unsteady-state conditions under cooling rates similar to those of found in industrial soldering practice. Examination of the resulting microstructures by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) permitted the different phases morphologies to be characterized: Bi-rich trigonal dendrites and long Zn fibers, as primary phases of, hypoeutectic and hypereutectic alloys, respectively, immersed in a fiber-like eutectic mixture. The combined effects of macrosegregation, Zn alloying and representative scales of the phases forming the microstructure (λint, λ2 and λE) on hardness of the Bi-Zn alloys are evaluated and Hall–Petch type equations relating λint, λ2 and λE to hardness are proposed78100110CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPNão temNão tem2017/15158-0The authors acknowledge the financial support provided by CAPES - Coordination for the Improvement of Higher Education Personnel, CNPq - The Brazilian Research Council and FAPESP - São Paulo Research Foundation, Brazil (grant 2017/15158-0). The authors would like to thank the Brazilian Nanotechnology National Laboratory – LNNano for the use of its facilitie

Electrochemical corrosion behavior of as-cast zn-rich zn-mg alloys in a 0.06m nacl solution

The electrochemical corrosion behavior of as-cast samples of Zn- 1.2 wt.% and Zn- 2.0 wt.% Mg alloys, solidified under similar cooling rates, is investigated in the present study. A stagnant and naturally aerated 0.06 M NaCl solution at 25 oC was used in the corrosion tests. In order to evaluate the corrosion resistance, electrochemical impedance spectroscopy (EIS) plots, potentiodynamic polarization curves and an equivalent circuit are used. It is found that the increase in the alloy Mg content (from 1.2wt.% to 2.0wt.%) refines both the Zn-rich dendritic matrix and the eutectic mixture and decreases the volume fraction of the Zn-rich phase. Consequently, this is shown to affect the cathode-to-anode area ratio, which decreases affecting the corrosion behavior. The experimental corrosion parameters demonstrated that the Mg content is associated with susceptibility to pitting corrosion1252645283CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPNão tem2013/23396-7; 2014/50502-5The authors acknowledge the financial support provided by FAEPEX-UNICAMP, CNPq - The Brazilian Research Council, FAPESP- São Paulo Research Foundation (grants 2013/23396-7 and 2014/50502-5), CNPEM and LNNano for the use of the X-Ray Diffaction (XRD) equipmen

Microstructure and tensile/corrosion properties relationships of directionally solidified al–cu–ni alloys

Al–Cu–Ni alloys are of scientific and technological interest due to high strength/high temperature applications, based on the reinforcement originated from the interaction between the Al-rich phase and intermetallic composites. The nature, morphology, size, volume fraction and dispersion of IMCs particles throughout the Al-rich matrix are important factors determining the resulting mechanical and chemical properties. The present work aims to evaluate the effect of the addition of 1wt%Ni into Al–5wt%Cu and Al–15wt%Cu alloys on the solidification rate, macrosegregation, microstructure features and the interrelations of such characteristics on tensile and corrosion properties. A directional solidification technique is used permitting a wide range of microstructural scales to be examined. Experimental growth laws relating the primary and secondary dendritic spacings to growth rate and solidification cooling rate are proposed, and Hall–Petch type equations are derived relating the ultimate tensile strength and elongation to the primary dendritic spacing. Considering a compromise between ultimate tensile strength and corrosion resistance of the examined alloys samples from both alloys castings it is shown that the samples having more refined microstructures are associated with the highest values of such properties24510581076CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DO AMAZONAS - FAPEAMNão temNão temThe authors acknowledge the financial support provided by CNPq—The Brazilian Research Council and FAPEAM–Amazonas State Research Support Foundation. The authors would like to thank the Brazilian Nanotechnology National Laboratory—LNNano for the use of its facilitie

Characterization of dendritic microstructure, intermetallic phases, and hardness of directionally solidified al-mg and al-mg-si alloys

Despite the widespread application of Al-Mg-Si alloys, especially in the automotive industry, interrelations of solidification thermal parameters (cooling rate and growth rate), microstructure, and hardness are not properly established. For instance, the control of the scale of the microstructure on both Al-Mg and Al-Mg-Si alloys by adequate pre-programming of the solidification thermal parameters remains a task to be accomplished. In the present study, the directional solidification (DS) of these alloys under unsteady-state solidification conditions is investigated in an attempt to characterize the evolution of microstructural features, macrosegregation, and hardness as a function of local solidification thermal parameters along the DS castings length. Silicon addition to the Al-Mg alloy was found not to affect the sizes of primary and secondary dendrite arm spacings, but induced the onset of tertiary dendritic branches and affected also the size and distribution of intermetallic particles within the interdendritic regions. The Al-Mg-Si alloy is characterized by a more complex arrangement of phases, including binary (α-Al + Mg2Si) and refined ternary (α-Al + Mg2Si + AlFe(Si) eutectic mixtures. As a consequence, a higher Vickers hardness profile is shown to be associated with the ternary Al-Mg-Si alloy DS casting. For both alloys examined, hardness is shown to increase with the increase in the microstructural spacing according to Hall–Petch type equations46833423355CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPNão tem2012/08494-0; 2012/16328-2; 2013/23396-7The authors acknowledge the financial support provided by FAPESP- São Paulo Research Foundation, Brazil (Grants 2012/08494-0; 2012/16328-2 and 2013/23396-7), FAEPEX-UNICAMP and CNPq (The Brazilian Research Council

Assessing Microstructure Tensile Properties Relationships in Al-7Si-Mg Alloys via Multiple Regression

The development of Al-based alloys presumes a detailed understanding of the microstructure evolution during solidification since the as-solidified microstructure also has effects on the subsequent thermo-mechanical processing. In the present investigation Al-7wt.%Si-xMg (x = 0.5 and 1 wt.%) alloys are subjected to transient directional solidification with a view to characterizing the microstructure evolution, with special focus on both dendritic evolution and the inherent features of the Mg2Si and π-AlSiFeMg intermetallics. Experimental power-type functions relating the primary, secondary and tertiary interdendritic spacings to the solidification cooling rate and growth rate are developed. It is observed that the Mg content added to the Al-7wt.%Si alloy and the consequent increase in the Mg2Si fraction tends to increase the values of the primary dendritic spacing. However, this same behavior is not verified for the growth evolution of dendritic side branches. A multiple linear regression (MLR) analysis is developed permitting quantitative correlations for the prediction of tensile properties and hardness from microstructural parameters to be established. The increase in the Mg alloy content from 0.5 to 1 was shown to promote an increase in both the ultimate tensile strength (σu) and elongation

Assessing Microstructure Tensile Properties Relationships in Al-7Si-Mg Alloys via Multiple Regression

The development of Al-based alloys presumes a detailed understanding of the microstructure evolution during solidification since the as-solidified microstructure also has effects on the subsequent thermo-mechanical processing. In the present investigation Al-7wt.%Si-xMg (x = 0.5 and 1 wt.%) alloys are subjected to transient directional solidification with a view to characterizing the microstructure evolution, with special focus on both dendritic evolution and the inherent features of the Mg2Si and π-AlSiFeMg intermetallics. Experimental power-type functions relating the primary, secondary and tertiary interdendritic spacings to the solidification cooling rate and growth rate are developed. It is observed that the Mg content added to the Al-7wt.%Si alloy and the consequent increase in the Mg2Si fraction tends to increase the values of the primary dendritic spacing. However, this same behavior is not verified for the growth evolution of dendritic side branches. A multiple linear regression (MLR) analysis is developed permitting quantitative correlations for the prediction of tensile properties and hardness from microstructural parameters to be established. The increase in the Mg alloy content from 0.5 to 1 was shown to promote an increase in both the ultimate tensile strength (σu) and elongation

Directionally solidified dilute Zn-Mg alloys : correlation between microstructure and corrosion properties

Zinc–Magnesium (Zn–Mg) alloys have been addressed as potential biodegradable biomaterials. These alloys enable to overcome the main drawbacks of Mg, its high corrosion rate and hydrogen evolution. Moreover, homogeneous corrosion degradation is also an interesting issue to ensure the success of load-bearing biodegradable implants. In this work, two directionally solidified dilute alloys, Zn-0.3wt-%Mg and Zn-0.5wt-%Mg were studied. Both alloys having different microstructural morphologies (cellular and dendritic arrays) depending of the distance to the cooling bottom were evaluated to correlate their microstructural features with corrosion properties. Kinetics and corrosion mechanism have been evaluated by means of DC and AC electrochemical techniques in low chloride containing solution, 0.06 M NaCl. Coarser microstructures are shown to promote higher corrosion rate. Like Zn the corrosion mechanism occurs throughout a multistep dissolution process involving the formation of intermediate monovalent ZnI, and soluble zinc hydroxychloride compounds resulting of the reaction of zincate ions with chloride ions723536547CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPNão temNão tem2012/16328-2; 2013/15478-3; 2013/23396-7; 2014/50502-

Directionally solidified dilute Zn-Mg alloys: Correlation between microstructure and corrosion properties

ZinceMagnesium (Zn-Mg) alloys have been addressed as potential biodegradable biomaterials. These alloys enable to overcome the main drawbacks of Mg, its high corrosion rate and hydrogen evolution. Moreover, homogeneous corrosion degradation is also an interesting issue to ensure the success of load-bearing biodegradable implants. In this work, two directionally solidified dilute alloys, Zn-0.3wt-% Mg and Zn-0.5wt-%Mg were studied. Both alloys having different microstructural morphologies (cellular and dendritic arrays) depending of the distance to the cooling bottom were evaluated to correlate their microstructural features with corrosion properties. Kinetics and corrosion mechanism have been evaluated by means of DC and AC electrochemical techniques in low chloride containing solution, 0.06 M NaCl. Coarser microstructures are shown to promote higher corrosion rate. Like Zn the corrosion mechanism occurs throughout a multistep dissolution process involving the formation of intermediate monovalent Zn-I, and soluble zinc hydroxychloride compounds resulting of the reaction of zincate ions with chloride ions. (C) 2017 Elsevier B.V. All rights reserved.FAPESP-Sao Paulo Research Foundation, BrazilCNPq - The Brazilian Research CouncilCAPESCSIC-Spanish National Research CouncilUniv Estadual Campinas, UNICAMP, Dept Mfg & Mat Engn, BR-13083860 Campinas, SP, BrazilCSIC, CENIM, Natl Ctr Met Res, Avda Gregorio del Amo 8, Madrid 28040, SpainUniv Fed Sao Paulo, UNIFESP, Marine Inst, BR-11030400 Santos, SP, BrazilUniv Fed Sao Paulo, UNIFESP, Marine Inst, BR-11030400 Santos, SP, BrazilFAPESP: 2012/163282FAPESP: 2013/15478-3FAPESP: 2013/23396-7FAPESP: 2014/50502-5CSIC-Spanish National Research Council: i-link0944Web of Scienc