本文選題：金屬成形 + 電輔助成形�。� 參考：《大連理工大學(xué)》2016年博士論文

【摘要】：在金屬材料的塑性成形過程中通入電流,能夠顯著地提高金屬材料的延伸率,降低流動(dòng)應(yīng)力。根據(jù)這一特點(diǎn),開發(fā)出的電輔助成形技術(shù)以高效節(jié)能的特點(diǎn)逐漸受到工業(yè)界和學(xué)術(shù)界的重視,具有廣闊的發(fā)展前景。電流對(duì)金屬材料性能的影響主要由兩方面要素引起：一方面是電流產(chǎn)生的焦耳熱影響材料的熱力學(xué)性能；另一方面則是電流本身在不考慮溫度作用的情況下亦能夠引起材料應(yīng)力下降和伸長(zhǎng)率提高。后者被稱為純電致塑性效應(yīng),對(duì)該方向的研究在相關(guān)領(lǐng)域內(nèi)存在爭(zhēng)議,部分學(xué)者認(rèn)為并沒有電致塑性效應(yīng)的存在,僅僅是溫度本身的作用引起材料力學(xué)性能發(fā)生改變。為了更加深入地研究電流對(duì)金屬材料的影響,本文建立了一套新型電輔助拉伸測(cè)試系統(tǒng),提出了一種新的對(duì)比試驗(yàn)方法,研究電流對(duì)金屬材料的焦耳熱效應(yīng)和純電致塑性效應(yīng)的影響。本文完成的主要研究工作包括：(1)設(shè)計(jì)開展了連續(xù)電流作用下的電輔助拉伸試驗(yàn),研究了電流密度、晶粒尺寸和流動(dòng)應(yīng)力之間的影響關(guān)系。和相同溫度下的熱輔助拉伸試驗(yàn)結(jié)果相比,電流誘導(dǎo)下的金屬材料產(chǎn)生更低的應(yīng)力,并且流動(dòng)應(yīng)力隨著電流密度的增加而進(jìn)一步降低。通過對(duì)不同晶粒尺寸的銅合金進(jìn)行對(duì)比試驗(yàn),發(fā)現(xiàn)晶粒尺寸越小,流動(dòng)應(yīng)力越高,電流引起的流動(dòng)應(yīng)力幅值下降越大；對(duì)于鋁合金的試驗(yàn)結(jié)果表明,隨著電流密度的增加,通電引起的應(yīng)變率敏感指數(shù)值由負(fù)值變?yōu)檎挡⒊掷m(xù)上升,并且電流引起的應(yīng)變率敏感指數(shù)值顯著高于溫度引起的指數(shù)值。同時(shí),將電流對(duì)鋁合金塑性失穩(wěn)效應(yīng)(PLC效應(yīng))的影響和相同溫度下的應(yīng)力曲線比較,可以得出電流有助于消除鋁合金的鋸齒流變的結(jié)論。(2)設(shè)計(jì)開展了脈沖電流作用下的電輔助拉伸試驗(yàn),研究了相同溫度峰值下不同脈沖電流密度和流動(dòng)應(yīng)力之間的關(guān)系。研究結(jié)果表明,脈沖電流產(chǎn)生的峰值溫度引起銅合金產(chǎn)生應(yīng)力回復(fù);當(dāng)峰值溫度高于600℃時(shí),應(yīng)力回復(fù)值與初始屈服應(yīng)力值接近。鋁合金的試驗(yàn)結(jié)果揭示,在產(chǎn)生相同溫度的條件下,隨著脈沖電流密度的增加,雖然最大應(yīng)力值不會(huì)產(chǎn)生較大波動(dòng),但是脈沖電流會(huì)引起瞬時(shí)應(yīng)力幅值將下降,并且伸長(zhǎng)率顯著增加。這說明了電流對(duì)金屬材料有額外的作用。(3)建立了電輔助成形中適用于多種材料的熱效應(yīng)模型�？紤]連續(xù)電流作用的焦耳熱效應(yīng),建立與材料熔點(diǎn)相關(guān)的熱軟化參數(shù)和歸一化電流密度之間的關(guān)系。根據(jù)適用于多種材料的熱軟化模型,得到不同材料的電流密度敏感系數(shù),并有效解釋了金屬材料成形中的電流密度閾值。此外,建立了脈沖電流中金屬材料應(yīng)力幅值瞬時(shí)下降的預(yù)測(cè)模型,綜合考慮電流產(chǎn)生的焦耳熱效應(yīng)和材料本身的應(yīng)變強(qiáng)化作用,模擬整個(gè)拉伸區(qū)間的應(yīng)力幅值下降,與試驗(yàn)結(jié)果吻合。(4)揭示了金屬材料在連續(xù)電流和脈沖電流中的微觀組織演變規(guī)律,包括晶粒尺寸、晶界效應(yīng)、動(dòng)態(tài)再結(jié)晶和空洞長(zhǎng)大等。高電流密度下的連續(xù)電流拉伸試驗(yàn)結(jié)果顯示,晶界區(qū)域出現(xiàn)空洞和熔融現(xiàn)象,這種現(xiàn)象是由電流產(chǎn)生的不均勻焦耳熱和應(yīng)變誘導(dǎo)的晶界熔化產(chǎn)生。銅合金在拉伸過程中發(fā)生動(dòng)態(tài)再結(jié)晶,并在斷裂區(qū)域出現(xiàn)疑似等軸鑄態(tài)組織和粗大樹枝態(tài)組織。此外,電流有助于抑制鋁合金鋸齒流變的產(chǎn)生,是由電流在沉積物附近團(tuán)聚并促進(jìn)沉積物的擴(kuò)散引起的。(5)最后,本文提出了一種基于新型表面微紋理制造技術(shù)的電輔助微軋制成形工藝。該工藝將電流和微軋制技術(shù)結(jié)合起來,快速實(shí)現(xiàn)金屬表面微結(jié)構(gòu)的制造。通過試驗(yàn)和仿真分析對(duì)比研究了通電和未通電工藝下的成形力和軋制形狀。結(jié)果表明,采用電輔助微軋制成形技術(shù)得到的鋁合金表面成形深度高。通過單搭接頭的剪切強(qiáng)度試驗(yàn)發(fā)現(xiàn),含有微軋制表面的試樣粘接性能顯著強(qiáng)于未經(jīng)處理的試樣。
[Abstract]:In the plastic forming process of metal materials, the penetration of current can significantly increase the elongation of metal materials and reduce the flow stress. According to this characteristic, the developed electric auxiliary forming technology is gradually paid attention to in the industry and the academia with the characteristics of high efficiency and energy saving. It has a broad development prospect. The response is mainly caused by two factors: one is that the Joule heat generated by the current affects the thermodynamic properties of the material; on the other hand, the current itself can cause the decrease of the material stress and the increase of the elongation at the same time without considering the temperature. The latter is called the pure electric plastic effect, and the research on this direction is in the related field. In dispute, some scholars believe that there is no electroplastic effect, only the effect of temperature itself causes the mechanical properties of materials to change. In order to further study the influence of current on metal materials, a new type of electrical auxiliary tensile test system was established, and a new comparative test method was put forward to study electricity. The influence of the Joule heat effect and the pure electroplastic effect on the metal material is studied. The main research work completed in this paper includes: (1) the electric auxiliary tensile test under the action of continuous current is designed and carried out. The relationship between the current density, the grain size and the flow stress is studied. Compared with the metal material induced by current, the metal material produces lower stress and the flow stress is further reduced with the increase of current density. By comparing the copper alloys with different grain sizes, the smaller the grain size, the higher the flow stress, the greater the flow stress amplitude of the current, and the test knot for the aluminum alloy. The results show that, with the increase of current density, the strain rate sensitivity index value changes from negative to positive and continues to rise with the increase of current density, and the strain rate sensitivity index caused by current is significantly higher than that caused by temperature. At the same time, the effect of current on the plastic instability effect (PLC effect) of aluminum alloy and the stress curve at the same temperature are compared. The conclusion is that the current can help eliminate the sawtooth rheology of the aluminum alloy. (2) the electric auxiliary tensile test under the pulse current is designed and the relationship between the different pulse current density and the flow stress at the same temperature peak is studied. The results show that the peak temperature produced by the pulse current causes the stress of the copper alloy. When the peak temperature is higher than 600 C, the stress recovery value is close to the initial yield stress value. The experimental results of aluminum alloy show that the maximum stress value will not produce large fluctuation with the increase of the pulse current density at the same temperature, but the pulse current will cause the instantaneous stress amplitude to decrease, and the elongation will be extended. This shows a significant increase in the effect of current on metal materials. (3) a thermal effect model suitable for various materials in electric assisted forming is established. Considering the Joule heat effect of continuous current, the relationship between the heat softening parameters related to the melting point of material and the normalized current density is established. The current density sensitivity coefficient of different materials is obtained, and the current density threshold in metal forming is explained effectively. In addition, the prediction model of the instantaneous drop of stress amplitude in metal material in pulse current is established, and the Joule heat effect produced by the current and the strain strengthening effect of the material itself are taken into consideration, and the whole drawing is simulated. The stress amplitude of the interval decreases with the experimental results. (4) the microstructure evolution of the metal material in continuous current and pulse current is revealed, including grain size, grain boundary effect, dynamic recrystallization and cavity growth. The results of continuous current tensile test under high current density show that the grain boundary area appears cavity and melting phenomenon. This phenomenon is produced by the melting of the grain boundary caused by the uneven Joule heat and strain induced by the current. The dynamic recrystallization of the copper alloy during the stretching process and the appearance of the doubtful equal axis cast structure and the coarse branch structure in the fracture region. In addition, the current helps to suppress the formation of the aluminum alloy saw tooth flow, and the current is near the sediments. (5) finally, an electric assisted micro rolling process based on a new surface micro texture manufacturing technology is proposed. This process combines the current and the micro rolling technology to quickly manufacture the micro structure of the metal surface. Through the experiment and simulation analysis, the electricity and the unelectricity are compared and studied. The forming force and rolling shape under the process show that the surface forming depth of the aluminum alloy is high. It is found that the bonding property of the sample containing the micro rolling surface is better than that of the untreated sample.

【學(xué)位授予單位】：大連理工大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：TG113.25

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