熱處理對(duì)a356鋁合金組織結(jié)構(gòu)和力學(xué)性能的影響畢業(yè)論文外文翻譯

1、<p>　　中文3765字,2400單詞</p><p>　　Effect of heat treatment on microstructure and</p><p>　　tensile properties of A356 alloys</p><p>　　PENG Ji-hua1, TANG Xiao-long1, HE Jian-ting1, X

2、U De-ying2</p><p>　　1. School of Materials Science and Engineering, South China University of Technology,</p><p>　　Guangzhou 510640, China;</p><p>　　2. Institute of Nonferrous Metal

3、, Guangzhou Jinbang Nonferrous Co. Ltd., Guangzhou 510340, ChinaReceived 17 June 2010; accepted 15 August 2010</p><p><b>　　Abstract</b></p><p>　　Two heat treatments of A356 alloys wi

4、th combined addition of rare earth and strontium were conducted. T6 treatment is a long time treatment (solution at 535℃ for 4h + aging at 150℃ for 15 h). The other treatment is a short time treatment (solution at 550℃ f

5、or 2h + aging at 170℃ for 2h). The effects of heat treatment on microstructure and tensile properties of the Al-7%Si-0.3%Mg alloys were investigated by optical microscopy, scanning electronic microscopy and tension test.

6、 It is found that a 2 h</p><p>　　Key words: Al-Si casting alloys; heat treatment; tensile property; microstructural evolution</p><p>　　1 Introduction</p><p>　　The aging-hardenable c

7、ast aluminum alloys, such as A356, are being increasingly used in the automotive industry due to their relatively high specific strength and low cost, providing affordable improvements in fuel efficiency. Eutectic struct

8、ure of A390 can be refined and its properties can be improved by optimized heat treatment. T6 heat treatment is usually used to improve fracture toughness and yield strength. It is reported that those factors influencing

9、 the efficiency of heat treatment of A</p><p>　　The T6 heat treatment of Al-7Si-0.3 Mg alloy includes two steps: solution and artificial aging; the solution step is to achieve α(Al) saturated with Si and Mg

10、and spheroidized Si in eutectic zone, while the artificial aging is to achieve strengthening phase Mg2Si. Recently, it is shown that the spheroidization time of Si is dependant on solution temperature and the original Si

11、 particle size. A short solution treatment of 30 min at 540 or 550℃ is sufficient to achieve almost the same mechanical p</p><p>　　In our previous study, it was found that the microstructure of A356 alloy co

12、uld be optimized by the combination of Ti, B, Sr and RE, and the eutectic melting peak temperature was measured to be 574.4℃ by differential scanning calorimetry (DSC). In this study, using this alloy modified together w

13、ith Sr and RE, the effect of different heat treatments on the microstructure and its mechanical properties were investigated.</p><p>　　2 Experimental</p><p>　　Commercial pure aluminum and silico

14、n were melted in a resistance furnace. The alloy was refined using Al5TiB master alloy, modified using Al-10Sr and Al-10RE master alloys. The chemical composition of this A356 alloy ingot (Table 1) was checked by reading

15、 spectrometer SPECTROLAB. Before casting, the hydrogen content of about 0.25 cm3 per 100 g in the melt was measured by ELH-III (made in China). Four bars of 50 mm×70 mm×120 mm were machined from the same ingot

16、and heat-treated according to Table</p><p>　　Table 1 Chemical composition of A356 modified with Ti, Sr and RE (mass fraction, %)</p><p>　　Table 2 Heat treatments in this study </p><p

17、>　　Tensile specimens were machined from the heat treated bars. The tensile tests were performed using a screw driven Instron tensile testing machine in air at room temperature. The cross-head speed was 1mm/min. The st

18、rain was measured by using an extensometer attached to the sample and with a measuring length of 50 mm. The 0.2% proof stress was used as the yield stress of alloys. Three samples were tested for each heat treatment to c

19、alculate the mean value.</p><p>　　3 Results and discussion</p><p>　　3.1 Microstructural characterization of as-cast alloy </p><p>　　The microstructure of as-cast A356 alloy is shown

20、 in Fig. 1(a). It is shown that not only the primary α(Al) dendrite cell is refined, but also the eutectic silicon is modified well. By means of the image analysis, microstructure parameters of as-cast A356 alloy were an

21、alyzed statistically as follows: α(Al) dendrite cell size is 76.1 μm, silicon particle size is 2.2 μm×1.03 μm (length×width), and the ratio aspect of silicon is 2.13.</p><p>　　The distributions of

22、RE (mish metal rare earth, more than 65% La among them), Ti, Mg, and Sr in the area shown in Fig. 1(b) are presented in Figs. 1(c)?(f) respectively. It is shown that the eutectic silicon particle is usually covered with

23、Sr, which plays a key role in Si particle modification; Ti and RE present generally uniform distribution over the area observed, although a little segregation of RE is observed and shown by arrow in Fig. 1(d). It is sugg

24、ested that because the refiner TiAl3 an</p><p>　　Ti solute can limit the growth of α(Al) primary dendrite because of its high growth restriction factor. The impediment of formation of poisoning Ti-Si compoun

25、d around TiAl3 and promotion of Ti(Al1?xSix)3 film covering TiB2 are very important in Al-Si alloy refining. For Al-Si alloys, the effect of RE on the refining efficiency of Ti and B can be contributed to the following c

26、auses: preventing refiner phases from poisoning; retarding TiB2 phase to amass and sink; promoting the Ti(Al, Si)3 compoun</p><p>　　3.2 Microstructural evolution during heat treatment</p><p>　　T

27、he microstructures of A356 alloys treated with solution at 550℃ for 2 h and ST treatment are presented in Figs. 2(a) and (b) respectively, while those treated with solution at 535℃for 4 h and T6 treatment are presented i

28、n Figs. 2(c) and (d), respectively. From Fig. 1 and Fig. 2, after different heat treatments, the primary α(Al) has been to some extent and the eutectic silicon has been spheroidized further. Both ST and T6 treatments pro

29、duce almost the same microstructure. The eutectic Si partic</p><p>　　The eutectic melting onset temperature of Al-7Si-Mg was reported to be more than 560 ℃.550℃ is below the liquid+solid phase zone. During s

30、olution, two steps occur simultaneously, i.e., the formation of Al solution saturated with Si and Mg, and spheroidization of fibrous Si particle. The following model predicts that disintegration and spheroidization of eu

31、tectic silicon corals are finished at 540℃ after a few minutes (τmax):</p><p><b>　　(1)</b></p><p>　　where φ denotes the atomic diameter of silicon; γ symbolizes the interfacial energ

32、y of the Al/Si interface; ρ is the original radius of fibrous Si; Ds is the inter-diffusion coefficient of Si in Al; and T is the solution temperature. When the Ds variation at different temperatures is taken into accoun

33、t, it is plausible to suggest that τmax at 550℃ is less than τmax at 540℃. From Fig. 2(a), it is actually proved that spheroidization of eutectic Si particle could be finished within 2 h when soluti</p><p>　

34、　In a selected area of A356 alloy treated with only solution at 550℃ for 2 h (Fig. 4(a)), the distribution of element Mg is presented in Fig. 4(b). Because there is no cluster of Mg in Fig. 4(b), it means a complete diss

35、olution of Si, Mg into Al dendrite during this solution. From the microstructure of A356 alloy treated with T6 (Fig. 5(a)), the distribution of Mg is shown in Fig. 5(b).</p><p>　　Fig. 1 SEM images (a, b), an

36、d EDS mapping from (b) for Ti (c), La (d), Mg (e) and Sr (f) in as-cast alloy</p><p>　　Fig. 2 Microstructure of A356 alloy with different heat treatments: (a) Solution at 550 °C for 2 h; (b) ST treatmen

37、t; (c) Solution at 535 °C for 4 h; (d) T6 treatment</p><p>　　For A357 alloy with dendrite size of 240 μm, uniform diffusion and saturation of Mg in Al could be finished at 540 °C within 2 h. In thi

38、s study, the cell size of primary α(Al) is less than 100 μm. It is reasonable that those solutions treated at 535 °C for 4 h and 550 °C for 2 h, can achieve α(Al) solid solution saturated with Mg and Si because

39、 diffusion route is short, even at a higher solution temperature.</p><p>　　Fig. 3 Statistic analysis of eutectic Si in A356 alloy with different heat treatments</p><p>　　Fig. 4 SEM image (a) and

40、 EDS mapping (b) of Mg distribution in alloy after only solution at 550℃for 2h</p><p>　　Fig. 5 SEM image (a) and EDS mapping of Mg (b) in alloy after heat treatment with T6</p><p>　　During aging

41、, Si and Mg2Si phase precipitation happened in the saturated solid solution of α(Al) according to the sequence in the Al-Mg-Si alloys with excess Si [21]. The needle shaped Mg2Si precipitation was observed to be about 0.

42、5 μm in length and less than 50 nm in width, and the silicon precipitates were mainly distributed in α(Al) dendrites and few of them could be observed in the eutectic region [22]. Because of the small size, these precipi

43、tations could not be observed by SEM in this stu</p><p>　　3.3 Tensile properties of A356 alloys</p><p>　　The tensile mechanical properties of A356 alloys are given in Table 3. Due to the microst

44、ructure optimization of A356 alloy by means of combination of refining and modification, tensile strength and fracture elongation can reach about 210 MPa and 3.7% respectively. Using T6 treatment in this study, strength

45、and elongation can be improved significantly. For those samples with T6 treatment, the tensile strength and ductility present the maximum values. 90% of the maximum yield strength, 95% of the</p><p>　　Table

46、3 Tensile properties of A356 alloys with different heat treatments</p><p>　　It is well known that shrinkage pores have a great effect on the tensile strength and ductility of A356 alloys. In-situ SEM fractur

47、e of A356 alloy indicates the fracture sequence as follows [4]: micro-crack initiation inside silicon particle; formation of slipping band in the Al dendrite; linkage between the macro-crack and micro-crack, and the grow

48、th of crack. During tensile strain, inhomogeneous deformation in the microstructure induces internal stresses in the eutectic silicon and Fe-bearing </p><p>　　Fig. 6 Fractographs of samples with different he

49、at treatments: (a), (b) T6; (c), (d) ST</p><p>　　4 Conclusions</p><p>　　1) The solution at 535 °C for 4 h and the solution at 550 °C for 2 h can reach full spheroidization of Si partic

50、le, over saturation of Si and Mg in α(Al). The heat treatments of T6 and ST produce almost the same microstructure of A356 alloy.</p><p>　　2) After both T6 and ST treatments, the aspect ratio of eutectic Si

51、particle will be reduced from 2.13 to less than 1.6, and the friction of eutectic Si particles with aspect ratio of 1.5 is 50%.</p><p>　　3) The T6 treatment can make the maximum strength and fracture elongat

52、ion for A356 alloy. After ST treatment, 90% of the maximum yield strength, 95% of the maximum ultimate strength, and 80% of the maximum elongation can be achieved.</p><p>　　熱處理對(duì)A356 鋁合金組織結(jié)構(gòu)和力學(xué)性能的影響</p>

53、<p>　　彭繼華1，唐小龍1，何健亭1，許德英2</p><p>　　1. 華南理工大學(xué) 材料科學(xué)與工程學(xué)院，廣州 510640；</p><p>　　2. 廣州金邦有色合金有限公司 有色金屬研究所，廣州 510340</p><p><b>　　摘 要</b></p><p>　　用兩種不同的熱處理制度

54、對(duì)稀土和鍶綜合細(xì)化變質(zhì)的 A356 合金進(jìn)行處理，一種是長(zhǎng)時(shí)間標(biāo)準(zhǔn)處理制度T6(535 °C 固溶 4 h+150 °C 時(shí)效 15 h)，另一種是短時(shí)間的熱處理制度 ST(550 °C 固溶 2 h+170 °C 時(shí)效 2 h)。采用光學(xué)顯微鏡、掃描電鏡及室溫拉伸試驗(yàn)等手段分析熱處理制度對(duì) A356 合金微觀組織和拉伸力學(xué)性能的影響。結(jié)果表明：在 550 °C 下固溶 2 h 可以獲得

55、 Mg、Si 過飽和且分布均勻的 α(Al)固溶體，并使共晶硅相球化；再經(jīng) 170°C 人工時(shí)效 2 h 后，可以達(dá)到傳統(tǒng) T6 處理的時(shí)效析出效果。拉伸試驗(yàn)結(jié)果表明，A356 鋁合金經(jīng)傳統(tǒng) T6 處理得到了最高的拉伸強(qiáng)度和斷裂伸長(zhǎng)率；通過 ST 短時(shí)熱處理后，其拉伸強(qiáng)度、屈服強(qiáng)度及伸長(zhǎng)率分別可以達(dá)到T6處理時(shí)的 90%，95%和 80%。</p><p><b>　　1.說明</b&g

56、t;</p><p>　　時(shí)效硬化的鑄造鋁合金,如A356,越來越多地使用在汽車行業(yè)由于其相對(duì)較高的比強(qiáng)度和較低的成本,提供負(fù)擔(dān)得起的改善燃油效率。共晶結(jié)構(gòu)可以精煉A390及其性能可以通過熱處理優(yōu)化。T6熱處理通常用來提高斷裂韌性和屈服強(qiáng)度。據(jù)報(bào)道,這些因素影響了效率的熱處理亞共晶鋁硅合金不僅包括溫度和保溫時(shí)間, 但也鑄態(tài)微觀組織和合金添加有關(guān)。一些T6處理試驗(yàn)方法標(biāo)準(zhǔn)的A356合金是由中國(guó)、美國(guó)和日本制定的,他

57、們都接受了。然而,他們需要超過4 h為解決方案在540°C,超過6小時(shí)在150°C的時(shí)效,從而導(dǎo)致大量能源消耗和低生產(chǎn)效率。它是縮短了熱處理保溫時(shí)間的好學(xué)習(xí)方法。</p><p>　　T6熱處理的Al - 7 - Si - 0.3鎂合金包括兩個(gè)步驟:解決方案和人工時(shí)效；解決方案步驟是實(shí)現(xiàn)α(Al)飽和與Si和Mg和球化處理Si在共晶區(qū),而人工時(shí)效強(qiáng)化相Mg2Si是實(shí)現(xiàn)。最近,它表明球化時(shí)間的S

58、i是依賴于溶液溫度和原始硅顆粒大小。一個(gè)短的解決方案在540或550°C處理30分鐘就足以實(shí)現(xiàn)處理6 h的解決方案幾乎相同的力學(xué)性能水平。從熱擴(kuò)散計(jì)算和測(cè)試,建議最優(yōu)方案是在540°C的處理時(shí)間為2h。最大峰值老化時(shí)間是建模方面的時(shí)效溫度和活化能。根據(jù)這個(gè)模型,A356合金的屈服強(qiáng)度峰值可以達(dá)到在2?4 h在170°C時(shí)效。然而,很少有研究的影響與短期解決方案和短期時(shí)效。</p><p&

59、gt;　　在我們先前的研究中,人們發(fā)現(xiàn)合金的顯微結(jié)構(gòu)結(jié)合Ti,B Sr和RE可以優(yōu)化A356,共晶熔化峰值溫度通過差示掃描量熱法(DSC)測(cè)量是574.4°C。在這項(xiàng)研究中,使用這種合金改性連同Sr和RE,作用不同的熱處理對(duì)微觀結(jié)構(gòu)及其力學(xué)性能進(jìn)行了調(diào)查。</p><p><b>　　2.試驗(yàn)</b></p><p>　　商業(yè)純的鋁和硅的電阻爐中熔化。合金細(xì)

60、化采用08期Al5TiB的主合金，修改使用的Al-10SR和鋁10RE中間合金。這個(gè)A356合金錠（表1）的化學(xué)成分直讀光譜儀SPECTROLAB檢查。在鑄造之前，約0.25立方厘米每100克在熔體中的氫含量ELH-III（中國(guó)制造）測(cè)定。從相同的錠的加熱處理，根據(jù)表2加工扶手為50毫米×70毫米×120毫米。其次該溶液中，在70℃的熱水中驟冷棒從鑄錠和熱處理后的棒切割的樣品進(jìn)行研磨，拋光和腐蝕，以0.5％HF劑。光

61、學(xué)顯微鏡徠卡-430和掃描電鏡LEO1530 VP與EDS（印加300）被用來研究的微觀結(jié)構(gòu)和斷口。為了量化不同的熱處理，共晶Si的形態(tài)變化的Image-Pro加6.0使用圖像分析儀，每次測(cè)量的800-1200顆粒。</p><p>　　表1 A356的化學(xué)成分改性與Ti，Sr和RE（質(zhì)量分?jǐn)?shù)，％）</p><p>　　表2在這項(xiàng)研究中的熱處理</p><p>　　

62、拉伸試樣加工從熱處理之后。拉伸試驗(yàn)，使用的螺桿驅(qū)動(dòng)的英斯特朗拉力試驗(yàn)機(jī)在室溫下在空氣中進(jìn)行。十字頭速度為1mm/分鐘。該菌株被測(cè)量通過使用附于該樣本的引伸和與測(cè)量的長(zhǎng)度為50毫米。作為合金的屈服應(yīng)力的0.2％彈性極限應(yīng)力。三個(gè)樣品進(jìn)行了測(cè)試的每個(gè)加熱處理來計(jì)算平均值。</p><p><b>　　3 結(jié)果與討論</b></p><p>　　3.1鑄態(tài)合金的顯微組織性質(zhì)

63、</p><p>　　圖1（a）為鑄態(tài)合金的鑄態(tài)A356合金的顯微組織的微結(jié)構(gòu)特征示。結(jié)果表明，不僅被提煉，初生α（Al）枝晶細(xì)胞也??共晶硅以及修改。通過圖像分析，鑄態(tài)A356合金的微結(jié)構(gòu)參數(shù)的統(tǒng)計(jì)分析如下：α（Al）枝晶單元大小為76.1微米，硅的粒徑為2.2微米×1.03微米（長(zhǎng)×寬），和比例硅方面是2.13。</p><p>　　RE（米什金屬稀土，其中La 6

64、5％以上），鈦，鎂，鍶圖所示的區(qū)域分布。圖1（b）顯示了存在的區(qū)域。圖1（c）-（F）分別呈現(xiàn)出來。它示出共晶硅粒子通常被鍶覆蓋，鍶在Si粒子改性Ti和RE目前觀察到的區(qū)域的大致均勻的分布起著關(guān)鍵的作用，雖然觀察到可再生能源的偏析不大，如圖中的箭頭所示。圖1（d）。有人建議，因?yàn)槟{TiAl3相和TiB2與RE覆蓋，精煉效率顯著提高。在鑄態(tài)合金中，Mg的若干個(gè)簇可能表明存在粗糙的Mg2Si的階段（箭頭所示，圖1（d））。</p&g

65、t;<p>　　鈦的溶質(zhì)可以限制的α（Al）枝晶的生長(zhǎng)，因?yàn)槠涓咴鲩L(zhǎng)的制約因素。周圍改性的Ti-Si化合物的形成TiAl3的障礙和促進(jìn)鈦（AL1-xSix）3薄膜覆蓋硼化鈦在Al-Si合金精煉中是非常重要的。鋁硅合金，Ti和B的煉油效率的影響稀土對(duì)可導(dǎo)致以下原因：防止改性;煉油階段延緩TiB2階段積累和吸收，促進(jìn)鈦（鋁，硅）3復(fù)合增長(zhǎng)率覆蓋硼化鈦相。在這項(xiàng)工作中，用合適的另外的Re和Sr，A356合金的微觀結(jié)構(gòu)是最佳的。尤

66、其，共晶Si的充分的修改，這是有益的，以促進(jìn)硅在固溶處理時(shí)進(jìn)一步球化。</p><p>　　3.2 熱處理過程中的微觀組織轉(zhuǎn)變</p><p>　　A356合金的顯微組織用溶液在550℃下2小時(shí)，ST處理圖圖2（a）及（b）分別為，而那些用溶液在535℃下4小時(shí)，T6處理的圖2（c）和（d）所示。從圖1和圖2，不同的熱處理后，初生α（Al）的已在一定程度上，共晶硅有進(jìn)一步球化。 ST和T6

67、治療產(chǎn)生幾乎相同的微觀結(jié)構(gòu)。共晶硅的顆粒分布和共晶Si粒子的統(tǒng)計(jì)平均縱橫比示于圖3。</p><p>　　圖1 SEM圖像(a,b),和EDS(b)映射為Ti(c)、La(d)、鎂(e)和Sr(f)在鑄態(tài)合金</p><p>　　固溶處理在535℃下4小時(shí)，550℃下進(jìn)行2小時(shí)后的Si的平均縱橫比分別為1.57和1.54。 ST和T6處理后的Si，這些縱橫比不變化很大，它們分別是1.49和

68、1.48，這項(xiàng)研究中在溶液或溶液+時(shí)效之后，共晶Si粒子的縱橫比為1.5的摩擦是50％。</p><p>　　據(jù)報(bào)道共晶熔融起始溫度Al-7Si-Mg，超過560°C。550°C以下的液體+固相區(qū)。在溶液過程中，兩個(gè)步驟同時(shí)進(jìn)行，即形成與Si和Mg的Al溶液飽和，纖維的Si顆粒的球化。下面的模型預(yù)測(cè)，共晶硅珊瑚的解體和球化完成在540°C后幾分鐘（τmax）：</p>

69、<p>　　式中，φ表示硅原子直徑;γ象征的Al/Si界面的界面能;ρ是纖維硅的初始半徑，Ds是在Al的Si的互擴(kuò)散系數(shù)，T為溶液的溫度。當(dāng)在不同溫度下的Ds的變化考慮在內(nèi)，這是合理的建議，τmax在550°C小于τmax在540℃。圖2（a）它實(shí)際上是證明，溶液在550℃時(shí)，共晶Si粒子的球化，可以在2小時(shí)內(nèi)完成。</p><p>　　圖2不同微觀結(jié)構(gòu)的A356合金熱處理:(a)固溶在550

70、℃2 h;(b)ST處理;(C)固溶在535℃ 4 h;(d)T6處理</p><p>　　圖3共晶硅在A356合金與不同的熱處理的統(tǒng)計(jì)分析</p><p>　　圖4 合金在550℃下2小時(shí)后的SEM圖像（a）和EDS圖譜的（b）Mg的分布</p><p>　　在A356鋁合金的選定區(qū)域用固溶處理，在550℃下進(jìn)行2小時(shí)（圖4（a）），元素鎂的分布示于圖4（b）。圖

71、4（b）中，它表示成Al枝晶的硅，圖中的Mg因?yàn)闆]有群集，鎂完全溶解。從T6（圖5（a））</p><p>　　圖5 合金經(jīng)過熱處理和T6的SEM圖像(a)和EDS Mg(b)</p><p>　　對(duì)于A357合金枝晶的大小為240μm，均勻擴(kuò)散和飽和度的Mg在Al可以在540℃下在2小時(shí)內(nèi)完成。在這項(xiàng)研究中，初生α（Al）的細(xì)胞的大小是小于100μm。這是合理的，這些解決方案在535℃下

72、4小時(shí)，550℃下進(jìn)行2小時(shí)的處理，因?yàn)閿U(kuò)散路徑短，即使在一個(gè)較高的溶液溫度，可實(shí)現(xiàn)的α（Al）固溶Mg和Si的飽和。</p><p>　　在時(shí)效過程中，Si和Mg2Si相沉淀發(fā)生在飽和固溶體α（鋁）根據(jù)用過量的硅的Al-Mg-Si系合金中的序列。 Mg2Si的析出針狀觀察到約0.5μm的長(zhǎng)度和寬度小于50nm，和硅的析出物主要分布在α（Al）的枝晶和共晶區(qū)域中可觀察到他們很少。由于體積小，無法被觀察到這些沉淀通

73、過SEM在這項(xiàng)研究中。但是，它是合理的建議枝晶Al的細(xì)胞區(qū)和共晶區(qū)中的Mg的分布是均勻的（圖4（b）和圖5（b））。根據(jù)由羅梅奇謝弗的研究時(shí)達(dá)到峰值的產(chǎn)率，為2-4小時(shí)和12-14小時(shí)分別在170℃和150℃下。從150到190℃的時(shí)效溫度，峰值硬度HB110和HB120之間。因此，它被認(rèn)為在170℃下時(shí)效2小時(shí)和在150℃下15小時(shí)的時(shí)效產(chǎn)生幾乎相同的析出硬化。</p><p>　　3.3 A356合金的拉伸性

74、能</p><p>　　A356合金的拉伸力學(xué)性能列于表3。由于A356鋁合金微觀結(jié)構(gòu)優(yōu)化手段相結(jié)合的提煉和修改，拉伸強(qiáng)度和斷裂伸長(zhǎng)率可以達(dá)到約210 MPa和3.7％。使用在這項(xiàng)研究中的T6處理，可以顯著提高強(qiáng)度和伸長(zhǎng)率。對(duì)于那些與T6處理后的樣品，具有拉伸強(qiáng)度和延性的提出的最大的值。的最大屈服強(qiáng)度的90％，最大的極限強(qiáng)度的95％和80％的最大伸長(zhǎng)率可以達(dá)到接近樣品ST處理。然而，T6治療花費(fèi)約19小時(shí)，而ST

75、處理需要只有4小時(shí)左右。與T6處理的樣品的斷口形貌示于圖 6。凹坑的大小幾乎是相似的不同的熱處理，說明不同的熱處理，共晶硅粒子的大小和間距變化不大。收縮毛孔，斷裂表面上觀察到微裂紋內(nèi)的共晶硅粒子的硅粒子和裂紋之間的關(guān)系。</p><p>　　表3 不同的熱處理的A356合金的拉伸性能</p><p>　　眾所周知收縮氣孔A356合金的拉伸強(qiáng)度和延性的有很大的作用。在SEM原位斷裂 A356

76、合金表示斷裂序列如下：硅粒子的內(nèi)部微裂紋的萌生;鋁枝晶滑移帶的形成，宏觀裂紋和微裂紋之間的聯(lián)系，而且增長(zhǎng)破裂。在拉伸應(yīng)變，在微觀結(jié)構(gòu)中的不均勻變形誘導(dǎo)共晶硅和Fe-軸承金屬間化合物顆粒的內(nèi)部應(yīng)力。雖然在這項(xiàng)研究中達(dá)成了全面修改的共晶硅粒子與T6處理，這些處理的樣品，不執(zhí)行不如預(yù)期。主要的原因可能是由于氣體含量較高（每100克鋁0.25立方厘米），我們的下一步是開發(fā)一種新的手段來凈化的Al-Si合金，以進(jìn)一步提高其機(jī)械性能。</p&

77、gt;<p>　　圖6 不同熱處理的斷口形貌樣品：（a）,(b)T6;(c) ,( d)ST</p><p><b>　　4 結(jié)論</b></p><p>　　1）熱處理在535℃下4小時(shí)和在550℃下進(jìn)行2小時(shí)可達(dá)到充分球化的Si粒子，α（Al）的Si和Mg的過飽和。熱處理T6和ST生產(chǎn)A356合金微觀結(jié)構(gòu)幾乎相同。</p><p&