Infuence of solution treatment on microstructure,mechanical and corrosion properties of Mg-4Zn alloy

Hongmin Jia,Xiaohui Feng,Yuansheng Yang*

Institute of Metal Research,Chinese Academy of Sciences,Shenyang 110016,China

Infuence of solution treatment on microstructure,mechanical and corrosion properties of Mg-4Zn alloy

Hongmin Jia,Xiaohui Feng,Yuansheng Yang*

Institute of Metal Research,Chinese Academy of Sciences,Shenyang 110016,China

The solution treatment parameters,mechanical properties and corrosion behavior of binary Mg-4Zn alloy were investigated.The results showed that after the solution treatment at 335°C for 16 h,Mg-4Zn alloy had an ultimate tensile strength of 184.13 MPa and elongation of 9.43%. Furthermore,the corrosion resistance was evaluated by electrochemical measurements and immersion tests in 3.5%NaCl solution.The results revealed that the corrosion current density of the solution treatment Mg alloy was 11.2 μA/cm?2,it was lower than 15.8 μA/cm?2for the as-cast Mg alloy under the same conditions,which was greatly associated with the micro-cathode effect of the second phases.

Solution treatment;Magnesium alloy;Mechanical property;Corrosion behavior

1.Introduction

Magnesium alloys have attracted great attention as medical implant material and devices due to their low density,perfect biocompatibility and close mechanical properties to natural bone[1–3]and it is also naturally found in the human body, where it plays essential roles in metabolic pathway[4–7]. Various magnesium alloys have been researched as biodegradable materials,such as AZ31,AZ91,AE21,WE43,LAE442 and so on[8,9].Unfortunately,most of the reported biomedical magnesium alloys contain aluminum and/or rare earth elements.Many researches[10–13]have shown Al is harmful to neurons and osteoblasts and also associated with dementia and Alzheimer’s disease.The administration of RE could lead to hepatotoxicity[14].Song explored several Mg alloys,pointing out that Zn,Ca and Mn could be appropriate element for biomedical application[6].It was also found that zinc was one of the most abundant nutritionally essential elements in the human body and had basic safety for biomedical application[12]. Therefore,Zn-containing Mg alloys have been paid more attention and developed as promising biomaterials.

However,the application of Mg alloys has been limited due to their high corrosion rate at physiological conditions and their fast biodegradation before the new tissue has adequately been healed[15].The early researches[16–21]have indicated that the poor corrosion resistance of Mg alloys mainly results from two reasons:The frst is the intrinsic dissolution tendency of magnesium,which is only weakly inhibited by corrosion product flms;the second is the presence of second phases acting as local cathodes and thus causing local micro-galvanic to accelerate corrosion[15].The effect of second phases on the corrosion resistance of Mg alloys has been investigated widely [22–27],especially for theAZ91 Mg alloys.The second phases usually act as cathodes to accelerate corrosion,while they may act as barrier against corrosion if they are in the form of continuous network along grain boundaries.In general,heat treatment is the most effective method to adjust the second phases, corresponding to change in the properties of Mg alloys[23].In this paper,the most suitable parameter of solution treatment is discussed and the effects of solution treatment on mechanical and corrosion properties of Mg-4Zn alloy as a degradable biomaterial are investigated to clarify the role of second phases in the corrosion mechanism.

2.Experimental

Ingots with nominal alloy compositions of Mg-4wt%Zn alloy were prepared with pure magnesium(99.99 wt%)and pure zinc(99.99 wt%)in an electronic resistance furnace underthe protection of CO2and 0.8%SF6mixture gas.The alloying melt was held at 730°C for 30 minutes to homogenize,and cast as ingots at 690°C into a graphite mold.The chemical compositions of the alloy were measured by inductively coupled plasma atomic emission spectrum (ICP-AES) apparatus.

還好，我腦海中不斷顯現(xiàn)的尷尬局面并沒(méi)有在第一天的傍晚出現(xiàn)，為第二天正式拍攝的探路工作在淺嘗輒止之后就結(jié)束了。而為了讓我在第二天不成為整個(gè)拍攝計(jì)劃的最主要障礙，牧馬人車(chē)主自告奮勇地開(kāi)始幫我復(fù)習(xí)曾在各種“冰雪試駕”和“越野體驗(yàn)”活動(dòng)中收獲的知識(shí)點(diǎn)。一番理論教授結(jié)束之后，在一群改頭換面的北汽BJ40、三菱帕杰羅的圍觀下，我成功依靠全新AMG G 63那充沛到有些過(guò)剩的動(dòng)力擺脫了一個(gè)因?yàn)榈纛^而陷入雪窩的尷尬。

Specimens cut from the ingots were frst solution treated with different times,then quenched into water.The temperature of solid solution was determined by the Mg-Zn binary phase diagram[28]and DSC analysis.Microstructures of specimens for different heat treatment times were observed with an optical microscope(OM).Vickers hardness testing was taken using 100 g load and holding time of 10 s,not fewer than 5 points were taken in each specimen.Tensile tests were performed at room temperature and a constant cross-head speed of 1 mm s?1. Three specimens were used for same test conditions to ensure the reproducibility of data.

[1]Y.F.Zheng,X.N.Gu,F.Witte,Mater.Sci.Eng.R 77(2014)1–34.

Samples for electrochemical test were cut from the ingots and mounted by epoxy resins with an exposed area of 1 cm2. The surface was grinded by 600–2000#SiC papers.The polarization test was carried out at room temperature in a beaker containing 3.5%NaCl solution using a standard three electrode confguration:the saturated calomel as a reference,a platinum electrode as the counter and the sample as the working electrode.In the polarization tests,the working electrode was frst immersed in NaCl solution for 5 minutes and then the polarization curve was measured at a scanning rate of 0.5 mV/s.

This work has been concerned with the solution treatment parameters,mechanical and corrosion properties.The main results can be summarized as follows.

3.Results and discussion

3.1.The optimum solution treatment parameters

The optical microstructure and XRD results of the as-cast Mg-4Zn alloy are shown in Fig.1.It can be seen that there were two main phases in the as-cast samples,namely,the matrix α phase and the second phases MgZn,precipitating along the grain boundary.

The DSC curves of the Mg-4Zn alloy are shown in Fig.2,the second phases dissolve at 346°C and exist steadily below 329°C.So the solid solution treatment temperature wasdetermined at 335°C in consideration of the furnace temperature fuctuation.

（一）在主推品種方面 武隆縣在肉牛產(chǎn)業(yè)發(fā)展中，主推西門(mén)塔爾牛和安格斯牛，首先用西門(mén)塔爾牛冷凍精液配種川南山地黃牛經(jīng)產(chǎn)母牛，再用安格斯牛凍精配種“西雜?！?，并將“紅西本”三雜牛作為商品牛進(jìn)行育肥出售。

Fig.1.Microstructure of the as-cast Mg-4Zn alloy and XRD result.

Fig.2.The DSC curve of Mg-4Zn alloy.

The curve of micro-hardness variation of the Mg-4Zn alloy for solution treatment at 335°C with time is shown in Fig.3. The hardness values are increased as solution time and reached a peak at 16 h,then the hardness started to decrease gradually. The change of the hardness can be explained through the microstructures during the solution treatment which are shown in Fig.4.It can be seen from Fig.4a and b that the microstructures contain a large number of second phases and the second phases become more dissolved into the Mg matrix with the increasing solution time(Fig.4c).By a solution time of 16 h,the second phases are dissolved completely(Fig.4d)and the alloy has a supersaturated single phase.There is a noticeable coarsening tendency of the grains in the following time(Fig.4e and f) compared with that of the original microstructure.As a result, the optimum solution parameter should be 335°C for 16 h for the Mg-4Zn alloy in the experiments.

Fig.3.Variation of the micro-hardness with solution time.

3.2.The effect of solution treatment on the mechanical properties

古往今來(lái)，傳統(tǒng)文化一直是我們?nèi)粘Ｉ钪械囊徊糠郑灤┝宋覀兠總€(gè)人的人生階段，它是無(wú)形的，亦是有形的。但如何理解這份傳統(tǒng)文化呢？

The tensile properties of the as-cast Mg-4Zn alloy in comparison with solution treatment Mg alloy are summarized in Table 1.The ultimate tensile strength(UTS)and elongation of the as-cast Mg alloy are 156.93 MPa and 7.38%,respectively. However,after the solution treatment,the UTS and elongation increased to 184.13 MPa and 9.43%,respectively.The enhancement of UTS is due to the solution strength effects of the alloying elements.Besides,Zn dissolving into Mg matrix will decrease the stacking fault energy of the matrix,which leads to the change of plastic deformation mechanism,i.e.,cross slip is diffcult to happen and twins will appear to adjust plastic deformation[29].Thus,the solution treatment will enhance the UTS and elongation at the same time.

The SEM micrographs of the fracture surface of the Mg-4Zn alloy are illustrated in Fig.5.The fracture surface consists of cleavage planes for the as-cast Mg-4Zn alloy(Fig.5a),which is in accordance with its lower elongation of 7.38%,so the fracture mold of as-cast Mg-4Zn alloy is quasi-cleavage.For the alloy subjected to solution treatment at 335°C,the fracture surface contains dimples and tear ridges(Fig.5b),which is in accordance with its higher elongation of 9.43%.But the fracture mold is also quasi-cleavage.

目前我國(guó)人民銀行、存款保險(xiǎn)基金管理機(jī)構(gòu)、銀監(jiān)部門(mén)都可以依法對(duì)問(wèn)題銀行采取早期糾正和風(fēng)險(xiǎn)處置措施，省級(jí)地方政府對(duì)農(nóng)信社負(fù)有管理責(zé)任和風(fēng)險(xiǎn)處置責(zé)任?？山⒋婵畋ｋU(xiǎn)管理機(jī)構(gòu)、人民銀行、銀行業(yè)監(jiān)管管理機(jī)構(gòu)、省級(jí)地方政府等共同參與的問(wèn)題銀行市場(chǎng)退出磋商機(jī)制，加強(qiáng)監(jiān)管協(xié)調(diào)和信息共享，強(qiáng)化協(xié)同推進(jìn)，提高問(wèn)題銀行風(fēng)險(xiǎn)處置的效率。此外，還應(yīng)進(jìn)一步明確存款保險(xiǎn)管理機(jī)構(gòu)運(yùn)用存款保險(xiǎn)基金參與問(wèn)題銀行接管、重整、破產(chǎn)等風(fēng)險(xiǎn)處置的形式和職責(zé)范圍，加強(qiáng)相關(guān)法律法規(guī)之間的有效銜接，完善問(wèn)題銀行市場(chǎng)化退出機(jī)制。

[18]A.Andrej,M.Liu,Z.A.Ishida,Mater.Sci.Eng.B 176(2011)1609–1636.

(1)The Mg-4Zn alloy was fabricated with high-purity raw materials and though DSC analysis,micro-hardness testing and microstructure observation,the optimum solution parameter is 335°C for 16 h.

Table 1Mechanical properties of Mg-4Zn alloy at room temperature.

Fig.4.Optical images of Mg-4Zn alloy during different solution time:(a)4 h,(b)8 h,(c)12 h,(d)16 h,(e)20 h,(f)24 h.

[3]G.L.Song,A.Andrej,D.H.St John,X.D.Wu,Corros.Sci.39(1997) 1981–2004.

老杜家不遠(yuǎn)。一到小區(qū)大門(mén)，老杜就活泛起來(lái)，忙不迭地下車(chē)?？粗⌒?qiáng)的車(chē)駛離，老杜呸地吐出一口痰：“畜生。”

Table 2Electrochemical parameters of Mg-4Zn alloy.

Fig.5.Typical fracture and SEM images:(a)as-cast,(b)335°C solid solution.

Fig.6.Polarization curves of the Mg alloy specimens in 3.5%NaCl solution.

As confrmed in the microstructure characterization of the as-cast and as-solution treatment specimens,the signifcant difference in microstructure between them is the second phases.In general,the second phases have nobler potential than the Mg matrix,so they may act as micro-cathode and the Mg matrix as the anode,resulting in galvanic corrosion.For the as-cast Mg-4Zn alloy in this experiment,the second phase particles MgZn can be regarded as the cathode sites and Mg matrix as the micro anode site.Thus,a lot of reactions happened on the surface of the samples,which resulted in an accelerated corrosion.Meanwhile,as to the solution treatment Mg-4Zn alloy,all the second phase particles were dissolved in the Mg matrix and less local reactions happen,so the sample surface experiences a uniform corrosion,resulting in a lower corrosion rate.

4.Conclusion

Immersion tests were also carried out according to ASTMG31-72[23]and the ratio of surface area to solution volume was 1 cm2:20 mL.Samples were removed for characterization after 4 h,12 h,24 h and 48 h of immersion in 3.5%NaCl solution,rinsed with distilled water and dried in air.The solution was refreshed at 12 h intervals to ensure the solution concentration unchanged.The corrosion products were cleaned with chromate acid(200 g/L CrO3 and 10 g/L AgNO3)for 1–2 minutes without removing any amount of metallic Mg,then washed with distilled water and alcohol,dried in air.The surface morphology after immersion was observed using scanning electron microscopy(SEM).

大豆根系作為大豆的重要器官之一，在大豆整個(gè)生長(zhǎng)發(fā)育、生理功能和物質(zhì)代謝中發(fā)揮著重要作用。由于根系生長(zhǎng)環(huán)境的特殊性，使得作物根系的研究遠(yuǎn)遠(yuǎn)滯后于地上部分，虛擬植物克服了傳統(tǒng)方式下試驗(yàn)周期長(zhǎng)、環(huán)境因素難以控制的缺點(diǎn)，大豆根系的虛擬研究具有重要現(xiàn)實(shí)意義。

The polarization curves of the as-cast Mg alloy and solution treatment Mg alloy in 3.5%NaCl solution are shown in Fig.6. The corrosion parameters obtained from the polarization curves are listed in Table 2.It can be seen that the corrosion potential shifts toward nobler direction and the corrosion current density of solution treatment Mg alloy is 11.2 μA/cm?2,lower than thatof the as-cast Mg alloy(15.8 μA/cm?2),which is related with the second phases in the as-cast alloys.

(2)The UTS and elongation of the solution treatment Mg-4Zn alloy were about 184.13 MPa and 9.43%, respectively.The fracture mold of the Mg-4Zn alloy was quasi-cleavage and it was not changed by solution treatment.

（10）Patent Litigation,Personal Jurisdiction,and the Public Good譯文：專(zhuān)利訴訟、屬人管轄和公共產(chǎn)品。

(3)The corrosion resistance of solution treatment samples is superior to the as-cast ones.The corrosion morphologies and immersion testing as well as electrochemical measurements proved that the corrosion resistance is strongly associated with the second phases,which act as the micro-cathodes to accelerate the corrosion of Mg matrix.

Fig.7.SEM micrographs of as-cast Mg-4Zn alloy.(a)4 h;(b)12 h;(c)24 h;(d)48 h.

Fig.8.SEM micrographs of solid solution Mg-4Zn alloy.(a)4 h;(b)12 h;(c)24 h;(d)48 h.

本文利用預(yù)應(yīng)力鋼絲繩對(duì)某座既有后張混凝土空心板梁橋進(jìn)行了加固，詳細(xì)介紹了該加固方法的實(shí)施步驟，并對(duì)加固前后的空心板進(jìn)行了荷載試驗(yàn)。通過(guò)對(duì)正常使用狀態(tài)下的荷載-撓度、裂縫寬度和鋼筋應(yīng)力進(jìn)行比較，明確了預(yù)應(yīng)力鋼絲繩對(duì)既有PC橋梁的加固效果。

[2]G.L.Song,A.Andrej,D.H.St John,J.Nairn,Y.Li,Corros.Sci.39(1997) 855–875.

The corrosion morphologies of the as-cast and as-solution treatment specimens of the Mg-4Zn alloy are observed to further clarify the effect of the second phases by immersion test in 3.5%NaCl solution,which are shown in Figs.7 and 8, respectively.In the early stage of immersion,a large number of hydrogen bubbles were evidently arising from the surface of theas-cast specimens indicating a fast rate of corrosion,compared to the solution treatment ones.After 4 h,the as-cast specimens were covered with corrosion products shown as Fig.7a,while only a small area of solution treatment specimens was covered with corrosion products(Fig.8a).As the immersion time increased,corrosion products were observed on all samples. With the immersion time increased to 48 h,there were a large number of deep pits as indicated by arrows shown in Figs.7d and 8d,respectively.However,the quantity and depth of the corrosion pits in the as-cast samples present a much larger scale compared with that in the solution treatment ones and these corrosion pits suggested that localized corrosion attacks happened during the immersion process.It was noted that the corrosion products were found on the bottom of beaker containing the as-cast specimens after immersion for 12 h.

[4]K.Y.Chiu,M.H.Wong,F.S.Cheng,H.C.Man,Surf.Coat.Tech.202 (2007)590–598.

[5]M.Jamesh,S.Kumar,Corros.Sci.53(2011)645–654.

1.規(guī)范管理，嚴(yán)格建立企業(yè)合格供應(yīng)商庫(kù)，優(yōu)化供貨渠道。企業(yè)應(yīng)實(shí)行供應(yīng)商準(zhǔn)入制度，從供應(yīng)商的供應(yīng)品種、經(jīng)營(yíng)規(guī)模大小、商業(yè)信用情況、發(fā)票開(kāi)具情況等多維度來(lái)進(jìn)行供應(yīng)商的篩選，其中同一品種的供應(yīng)商應(yīng)保證有三家至五家以滿(mǎn)足比質(zhì)比價(jià)的需求。如果供應(yīng)商在供應(yīng)原材料過(guò)程中發(fā)生質(zhì)量問(wèn)題、價(jià)格虛高或開(kāi)票不規(guī)范等情況，可以給予對(duì)方整改的機(jī)會(huì)，但如再次發(fā)生經(jīng)協(xié)調(diào)無(wú)果的，應(yīng)及時(shí)從企業(yè)供應(yīng)商名錄中刪除，以保證供應(yīng)商庫(kù)的質(zhì)量。供應(yīng)商庫(kù)每年應(yīng)進(jìn)行動(dòng)態(tài)管理，及時(shí)掌握供應(yīng)商的經(jīng)營(yíng)和信用等情況。特別是營(yíng)改增之后企業(yè)需要對(duì)經(jīng)營(yíng)不正規(guī)、不能提供所需發(fā)票的供應(yīng)商進(jìn)行剝離，從源頭上達(dá)到節(jié)稅的目的，同時(shí)對(duì)提高原材料質(zhì)量也有積極的促進(jìn)作用。

[6]G.L.Song,Corros.Sci.49(2007)1696–1701.

[7]S.X.Zhang,X.N.Zhang,C.L.Zhao,Acta Biomater.6(2010)626–640.

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[10]M.B.Yang,X.F.Liang,Z.Yi,F.S.Pan,Mater.Des.32(2011)1967–1973.

[11]X.B.Zhang,Z.Z.Wang,G.Y.Yuan,Y.J.Xue,Mater.Sci.Eng.B 177 (2012)1113–1119.

[12]X.N.Gu,N.Li,Y.F.Zheng,L.Q.Ruan,Mater.Sci.Eng.B 176(2011) 1778–1784.

[13]W.Zhang,M.Li,Q.Chen,M.Hu,Mater.Des.39(2012)379–383.

[14]S.X.Zhang,J.N.Li,Y.Song,C.L.Zhao,X.N.Zhang,C.Y.Xie,Mater. Sci.Eng.B 29(2009)1907–1912.

[15]Y.J.Chen,Z.G.Xu,C.Smith,J.Sankar,Acta Biomater.10(2014) 4561–4573.

[16]G.L.Song,S.Z.Song,Adv.Eng.Mater.9(2007)298–302.

新經(jīng)濟(jì)環(huán)境下對(duì)于中小制造企業(yè)不單是機(jī)會(huì)，也有不少挑戰(zhàn)，以往的問(wèn)題更加凸顯出來(lái)。中小企業(yè)應(yīng)當(dāng)意識(shí)到這些情況，同時(shí)積極應(yīng)對(duì)，適應(yīng)市場(chǎng)的演化，保持長(zhǎng)遠(yuǎn)健康成長(zhǎng)。

[17]M.Jamesh,S.Kumar,N.T.Sankara,Corros.Sci.53(2011)645–654.

3.3.The effect of solution treatment on corrosion properties

朋友此文寫(xiě)好后，為察納雅言、博取眾長(zhǎng)，將其發(fā)在一個(gè)不大的文友群里。湊巧看到，我便認(rèn)真拜讀。讀后，有所感，不吐不快，便在其后留評(píng)：這個(gè)故事文字流暢生動(dòng)，情節(jié)雖略缺新意，但曲折瑰麗，點(diǎn)贊之外，說(shuō)幾句不限于這篇文章的題外話——如果這美麗的傳說(shuō)，能借助文字而得以流傳，若干年后，我們的后代，會(huì)以為這片桃園，竟有如此神奇的來(lái)歷，但他們不會(huì)知道，這只是在公元21世紀(jì)之初，在蔚然成風(fēng)的人工造景熱潮中，悄然綻放的一朵小花，在桃園之前，這里曾是棉海糧倉(cāng)。倘如此，他們豈不會(huì)把他們某一代祖宗的功勞，錯(cuò)記到神仙頭上？要是他們從湊巧得到的歷史知識(shí)中知道了真相，那時(shí)，他們對(duì)我們這些已經(jīng)作古的編故事的祖宗，作何感想？

[19]Y.W.Song,E.H.Han,D.Y.Shan,Corros.Sci.65(2012)322–330.

[20]Y.W.Song,E.H.Han,D.Y.Shan,Corros.Sci.60(2012)238–245.

1）進(jìn)行參數(shù)化設(shè)計(jì)，新型技術(shù)需要滿(mǎn)足設(shè)計(jì)師對(duì)建筑信息的需求，BIM技術(shù)中應(yīng)用到的軟件可以將觀察到的對(duì)象信息設(shè)計(jì)成整體的結(jié)構(gòu)狀態(tài)；

[21]S.H.Cai,T.Lei,N.F.Li,Mater.Sci.Eng.C 32(2012)2570–2577.

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Received 4 May 2015;accepted 26 August 2015 Available online 1 October 2015

*Corresponding author.Institute of Metal Research,Chinese Academy of Sciences,Shenyang 110016,China.Tel.:+86 24 23971728;fax:+86 24 23844528.

E-mail address:ysyang@imr.ac.cn(Y.Yang).

http://dx.doi.org/10.1016/j.jma.2015.08.006

2213-9567/?2015 Production and hosting by Elsevier B.V.on behalf of Chongqing University.

?2015 Production and hosting by Elsevier B.V.on behalf of Chongqing University.