【摘要】：近年來,國內(nèi)外學(xué)者致力于研究改善鎂及鎂合金的強(qiáng)度和室溫變形能力。細(xì)晶強(qiáng)化是提高鎂合金室溫綜合性能最有效的途徑。經(jīng)過等徑角擠壓(ECAP)加工的鎂及鎂合金室溫綜合性能明顯提高。但由于鎂合金室溫塑性變形能力差且再結(jié)晶溫度低的特性,限制了ECAP工藝細(xì)化晶粒的效果。包套ECAP工藝是一種新型ECAP工藝有效解決了純鎂室溫下ECAP變形過程發(fā)生開裂的問題。但該工藝影響因素眾多,且模具內(nèi)部加工過程封閉,借助計(jì)算機(jī)仿真技術(shù)在很大程度上有效反映工件的變形行為。對于鎂合金ECAP過程的數(shù)值模擬研究,必須要準(zhǔn)確地預(yù)測工件的損傷程度,但現(xiàn)階段的模擬方法難以實(shí)現(xiàn)動態(tài)的損傷演化過程。本文使用光滑粒子流體動力學(xué)(SPH)方法來處理動態(tài)損傷演化問題,通過建立基于SPH方法含損傷預(yù)測模型的計(jì)算程序,對室溫下純鎂的ECAP過程和包套ECAP過程進(jìn)行模擬研究。主要研究工作和結(jié)論如下:首先,基于彈塑性力學(xué)的SPH方法建立了鎂及鎂合金ECAP變形過程的數(shù)學(xué)模型。通過修正SPH基本控制方程來保證計(jì)算過程的穩(wěn)定性,并采用罰函數(shù)排斥力來處理固壁邊界問題,移動邊界實(shí)現(xiàn)擠壓運(yùn)動過程。編寫了基于sph方法計(jì)算程序,通過計(jì)算經(jīng)典算例驗(yàn)證了本文所建計(jì)算程序的正確性,對200℃下az31鎂合金的ecap變形過程進(jìn)行了模擬計(jì)算,獲得了與有限元商業(yè)軟件基本一致的計(jì)算結(jié)果。為基于sph方法含損傷預(yù)測模型計(jì)算程序的建立奠定基礎(chǔ)。其次,針對材料的動態(tài)損傷演化問題,在上文已建程序的基礎(chǔ)上,加入損傷演化本構(gòu)模型和失效粒子法,編寫了基于sph方法含損傷預(yù)測模型的計(jì)算程序。通過對室溫下純鎂在不同擠壓速度下ecap損傷演化過程的模擬研究,并與已有試驗(yàn)結(jié)果的對比表明本文程序可以準(zhǔn)確模擬純鎂的損傷演化過程。模擬研究表明,高變形速率導(dǎo)致純鎂發(fā)生韌脆轉(zhuǎn)變,宏觀裂紋萌生之前,試樣中形成束狀高應(yīng)變率區(qū)逐漸匯聚于剪切面,并在裂紋擴(kuò)展至斷裂后消失;較低變形速率下純鎂呈片層狀開裂,損傷演化過程具有周期性,塑性變形區(qū)應(yīng)變率分布均勻性提高,裂紋擴(kuò)展緩解高應(yīng)變集中趨勢,裂尖周圍產(chǎn)生塑性變形阻礙裂紋擴(kuò)展。最后,使用本文所建基于sph方法含損傷預(yù)測模型的計(jì)算程序,對室溫下純鎂在兩種包套材料的ecap變形過程進(jìn)行了模擬研究。研究表明,同等擠壓條件下,以2024鋁合金為包套的組合工件發(fā)生片層狀開裂;以工業(yè)純鐵為包套的組合工件保持完整且擠壓過程中純鎂的變形均勻性明顯提高。
[Abstract]:In recent years, scholars at home and abroad have focused on improving the strength and room temperature deformability of magnesium and magnesium alloys. Fine grain strengthening is the most effective way to improve the comprehensive properties of magnesium alloys at room temperature. The comprehensive properties of magnesium and magnesium alloys processed by equal-diameter angular extrusion (ECAP) at room temperature are improved obviously. However, due to the poor plastic deformation at room temperature and low recrystallization temperature, the grain refinement effect of ECAP process is limited. The coated ECAP process is a new type of ECAP process which effectively solves the problem of cracking during ECAP deformation at room temperature of pure magnesium. However, there are many factors affecting the process, and the internal processing process of the die is closed, so the deformation behavior of the workpiece can be reflected to a great extent by computer simulation technology. For the numerical simulation of magnesium alloy ECAP process, it is necessary to accurately predict the damage degree of the workpiece, but the present simulation method is difficult to realize the dynamic damage evolution process. In this paper, the smooth particle hydrodynamics (SPH) method is used to deal with the dynamic damage evolution problem. The ECAP process and the wrapped ECAP process of pure magnesium at room temperature are simulated by establishing a program based on the SPH method with damage prediction model. The main work and conclusions are as follows: firstly, the mathematical model of ECAP deformation process of magnesium and magnesium alloys is established based on the SPH method of elastoplastic mechanics. The stability of the calculation process is guaranteed by modifying the SPH basic governing equation, and the penalty function repulsion force is used to deal with the problem of the solid wall boundary, and the moving boundary is used to realize the extrusion process. The calculation program based on sph method is compiled, and the correctness of the program is verified by calculating the classical example. The ecap deformation process of az31 magnesium alloy at 200 鈩，

本文編號：2228957