LZ91鎂鋰合金分流模擠壓成形過程數(shù)值模擬與實(shí)驗(yàn)研究

LZ91鎂鋰合金分流模擠壓成形過程數(shù)值模擬與實(shí)驗(yàn)研究Numerical Simulation and Experimental Study on Porthole Die Extrusion Process of LZ91 Mg-Li Alloy

分流模擠壓是生產(chǎn)空心型材的主要手段，具有生產(chǎn)效率高、可成形復(fù)雜截面型材等優(yōu)點(diǎn)。本文建立了LZ91鎂鋰合金分流模擠壓過程的有限元模擬模型，研究了擠壓比對(duì)型材擠壓過程中溫度、應(yīng)變、流動(dòng)速度等物理場(chǎng)量的影響規(guī)律，采用J準(zhǔn)則對(duì)型材的焊合質(zhì)量進(jìn)行了定量分析，并開展了不同擠壓比條件下的分流模擠壓實(shí)驗(yàn)，研究了鑄造態(tài)、均熱態(tài)、擠壓態(tài)LZ91鎂鋰合金的微觀組織特點(diǎn)。結(jié)果表明，在分流橋表面及其下部的材料處于大變形區(qū)，分流孔內(nèi)部的材料處于小變形區(qū)，且隨擠壓比增加，材料的應(yīng)變整體上升。受塑性變形熱和型材冷卻散熱等因素的影響，分流橋上端材料的溫度升高，但越靠近模具出口處材料的溫度越低。焊合質(zhì)量受多種因素的影響，焊縫中心位置處的焊合質(zhì)量低于焊縫邊緣處，而隨著擠壓比的增大，焊合質(zhì)量得到改善。焊縫區(qū)由于應(yīng)變較大，其再結(jié)晶形核數(shù)量多，生成的晶粒較細(xì)小，而基體區(qū)因動(dòng)態(tài)再結(jié)晶不夠充分，其晶粒比較粗大。當(dāng)擠壓比增大時(shí)，由于溫度升高，還發(fā)生了晶粒長大現(xiàn)象。

Porthole die extrusion is the dominant process to produce hollow profiles due to its high productivity and capacity in producing complex profiles. In this study, the finite element simulation model of porthole die extrusion of LZ91 Mg-Li alloy was established. The effects of extrusion ratio on strain, temperature, and flow velocity were studied, and the welding quality was quantitatively evaluated by means of J criterion. The experiments of porthole die extrusion were carried out by varying extrusion ratios. The microstructures of as-cast, homogenized and extruded LZ91 alloy were examined. The results show that the materials near the bridge surface and at the bottom of the bridge have large deformation, while the materials inside the portholes have small deformation. Moreover, with the increase of extrusion ratio, the effective strain of material is increased. Due to the heat generated by plastic deformation and the heat dissipation caused by profile cooling, the temperature of the material on the top of bridge is increased, and that of the material near the die exit becomes lower. The welding quality in the central area of weld seam is lower than that in the edge area of weld seam. With the increase of extrusion ratio, the welding quality is improved. More nucleation is generated in welding zone due to its large strain, resulting in the formation of fine grains. However, the dynamic recrystallization is not complete in the matrix zone, and some coarse grains still remain. Moreover, the material temperature becomes higher with high extrusion ratio, and the phenomenon of grain growth is observed.

全文下載：https://pan.baidu.com/s/1hsq0WJy