【摘要】：鎂合金因其優(yōu)良的物理力學(xué)性能,在航空、航天、軍工以及民用等領(lǐng)域應(yīng)用較為廣泛。目前,有關(guān)變形鎂合金大塑性變形技術(shù)的研究報(bào)道較多,但多數(shù)大塑性變形方法存在生產(chǎn)效率低、成本高、工藝復(fù)雜且無(wú)法實(shí)現(xiàn)連續(xù)生產(chǎn)等問題。本文研究了一種集正擠壓與多次彎曲剪切于一體的棒-板正擠壓-彎曲剪切復(fù)合連續(xù)成形新工藝(Direct Extrusion and Bending Shearing,DEBS)。以商用鑄態(tài)AZ31鎂合金為研究對(duì)象,通過塑性力學(xué)理論計(jì)算、有限元數(shù)值模擬以及實(shí)驗(yàn)等手段對(duì)該工藝進(jìn)行了多方面研究,主要包括:擠壓力、應(yīng)變和應(yīng)變率的理論計(jì)算;模具型腔設(shè)計(jì)及工藝參數(shù)優(yōu)化;DEBS鎂板力學(xué)性能和微觀組織的檢測(cè)與分析等等。所獲得的研究成果如下:(1)DEBS復(fù)合成形工藝的理論分析。將上界法和有限元數(shù)值模擬方法相結(jié)合,引入形狀復(fù)雜系數(shù),對(duì)棒-板正擠壓-彎曲剪切復(fù)合連續(xù)變形工藝所需的擠壓力及各階段的應(yīng)變、應(yīng)變率和變形速率因子(Z參數(shù))進(jìn)行了理論計(jì)算。通過試驗(yàn)研究驗(yàn)證了計(jì)算結(jié)果的可靠性,可為模具型腔設(shè)計(jì)及擠壓機(jī)型號(hào)的合理選擇提供理論指導(dǎo)。(2)DEBS模具型腔設(shè)計(jì)。以平均擠壓載荷Favg、速度場(chǎng)相對(duì)標(biāo)準(zhǔn)偏差VRSDV、應(yīng)變均值εavg和應(yīng)變相對(duì)標(biāo)準(zhǔn)偏差εRSDV為定量化評(píng)價(jià)指標(biāo),運(yùn)用DEFORM-3D有限元數(shù)值擬軟件對(duì)DEBS擠壓過程進(jìn)行了模擬分析,得出了各結(jié)構(gòu)參數(shù)對(duì)成形結(jié)果的影響規(guī)律。結(jié)果表明:對(duì)于DEBS復(fù)合擠壓工藝,當(dāng)錐角φ為120o、擠壓通道彎曲角β為150o、擠壓通道彎曲角Ψ為110o、擠壓通道彎曲過渡半徑R1為6 mm、定徑區(qū)長(zhǎng)度L5為12 mm時(shí),所獲得的的鎂合金板材(橫截面:25 mm×3 mm)質(zhì)量較佳。(3)DEBS工藝參數(shù)優(yōu)化。選用已設(shè)計(jì)好的DEBS模具作為研究基礎(chǔ),在不同的工藝條件下,采用有限元軟件對(duì)DEBS擠壓過程進(jìn)行了模擬分析,并研究了各工藝參數(shù)對(duì)成形結(jié)果的影響規(guī)律。研究結(jié)果表明:當(dāng)擠壓溫度為370℃、擠壓速度為2 mm·s-1時(shí),有利于保證板材的質(zhì)量。(4)實(shí)驗(yàn)驗(yàn)證與分析。在數(shù)值模擬分析結(jié)果的指導(dǎo)下,成功實(shí)現(xiàn)了DEBS擠壓試驗(yàn),并對(duì)DEBS鎂板的力學(xué)性能和微觀組織進(jìn)行了檢測(cè)分析。結(jié)果表明:(1)DEBS復(fù)合工藝可顯著地改善鎂合金的微觀組織與綜合力學(xué)性能。(2)當(dāng)擠壓溫度為370℃、擠壓速度為2 mm·s-1時(shí),經(jīng)一道次成形后平均晶粒尺寸由原始鑄態(tài)的240μm可細(xì)化至6μm以下,抗拉強(qiáng)度與屈服強(qiáng)度分別為300 MPa、220 MPa,室溫?cái)嗔蜒由炻士筛哌_(dá)25.7%,這也驗(yàn)證了工藝參數(shù)優(yōu)化結(jié)果的合理性。(3)由擠壓力測(cè)試值與數(shù)值模擬值對(duì)比分析可知,相對(duì)誤差在10%以內(nèi),可以滿足工程計(jì)算要求,驗(yàn)證了數(shù)值模擬結(jié)果的可靠性。
[Abstract]:Magnesium alloys are widely used in aviation, aerospace, military and civil fields due to their excellent physical and mechanical properties. At present, there are many reports about the large plastic deformation technology of wrought magnesium alloy, but most of the large plastic deformation methods have some problems such as low production efficiency, high cost, complicated process and unable to realize continuous production, and so on. In this paper, a new continuous forming process (Direct Extrusion and Bending Shearing,DEBS) of bar-sheet forward extrusion-bending shear combined with forward extrusion and multiple bending shear is studied. Taking commercial as-cast AZ31 magnesium alloy as research object, many aspects of the process were studied by means of plasticity theory calculation, finite element numerical simulation and experiment, including the theoretical calculation of extrusion pressure, strain and strain rate; Die cavity design and process parameters optimization; DEBS magnesium plate mechanical properties and microstructure detection and analysis, and so on. The research results are as follows: (1) theoretical analysis of DEBS composite forming process. Combining the upper bound method with the finite element numerical simulation method, the complex shape coefficient is introduced, and the extrusion pressure and the strain of each stage of the bar-plate extrusion-bending shear composite continuous deformation process are studied. The strain rate and deformation rate factor (Z parameter) are calculated theoretically. The reliability of the calculated results is verified by experimental research, which can provide theoretical guidance for die cavity design and reasonable selection of extruder type. (2) DEBS die cavity design. Taking Favg, velocity field relative standard deviation (VRSDV,) and strain relative standard deviation (蔚 RSDV) of average extrusion load as quantitative evaluation indexes, the process of DEBS extrusion is simulated and analyzed by DEFORM-3D finite element simulation software. The influence of structural parameters on the forming results is obtained. The results show that when the cone angle 蠁 is 120o, the extrusion channel bending angle 尾 is 150o, the extrusion channel bending angle is 110o, and the extrusion channel bending transition radius R1 is 6 mm, sizing zone length L5 is 12 mm. For DEBS composite extrusion process, the bending angle of extrusion channel is 110o, the bending angle of extrusion channel is 150o, the bending angle of extrusion channel is 110o. The obtained magnesium alloy sheet (cross section: 25 mm 脳 3 mm) is of better quality. (3) the process parameters of DEBS are optimized. Based on the designed DEBS die, the process of DEBS extrusion was simulated and analyzed by finite element software under different process conditions, and the influence of various process parameters on the forming results was studied. The results show that when the extrusion temperature is 370C and the extrusion speed is 2 mm 路s-1, the quality of the sheet is guaranteed. (4) the experimental verification and analysis are carried out. Under the guidance of numerical simulation and analysis, the DEBS extrusion test was successfully carried out, and the mechanical properties and microstructure of DEBS magnesium plate were tested and analyzed. The results show that: (1) the microstructure and comprehensive mechanical properties of magnesium alloy can be significantly improved by DEBS composite process. (2) when the extrusion temperature is 370C and the extrusion speed is 2 mm 路s-1, the microstructure and mechanical properties of magnesium alloy can be improved obviously. After one-pass forming, the average grain size can be refined from 240 渭 m to less than 6 渭 m, and the tensile strength and yield strength can be up to 25.7% at room temperature, respectively, when the tensile strength and yield strength are 300 MPa,220 MPa, respectively, and the average grain size can be refined from 240 渭 m to less than 6 渭 m. This also verifies the rationality of the optimization results of process parameters. (3) through the comparative analysis of extrusion pressure test values and numerical simulation values, the relative error is less than 10%, which can meet the requirements of engineering calculation and verify the reliability of numerical simulation results.
【學(xué)位授予單位】：湖南科技大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TG379

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