發(fā)布時(shí)間：2018-07-17 00:55

【摘要】：7000系列和2000系列鋁合金同屬于高強(qiáng)度鋁合金，廣泛用于航空航天領(lǐng)域，它們都有著“不可焊金屬”之稱。攪拌摩擦焊從根本上解決了高強(qiáng)鋁合金的難焊問題，實(shí)際焊接過程中焊接溫度以及金屬的塑性流動(dòng)對(duì)焊縫成型非常重要，因此關(guān)于兩種合金熱變形行為的研究對(duì)弄清焊接機(jī)理及焊接工藝優(yōu)化有重要意義。 本文采用物理模擬的方法，利用Gleeble-3500熱模擬機(jī)分別采用拉伸和壓縮的方法，系統(tǒng)地研究了7050和2024鋁合金的熱變形行為。從流變應(yīng)力上看，兩種合金的變化規(guī)律類似，，受應(yīng)變速率和溫度影響顯著�？傮w上流變應(yīng)力隨溫度的升高和應(yīng)變速率的降低而減小。 對(duì)于拉伸變形，以斷面收縮率和延伸率為塑性指標(biāo)結(jié)合金相組織照片，討論了溫度和應(yīng)變速率對(duì)金屬塑性的影響，并建立了熱變形本構(gòu)方程。結(jié)果表明：兩種合金塑性都隨著變形溫度的升高及應(yīng)變速率的降低而升高。7050鋁合金與2024鋁合金相比，熱變形激活能Q更小，這說明前者更容易發(fā)生動(dòng)態(tài)再結(jié)晶。實(shí)驗(yàn)條件下，7050鋁合金主要軟化機(jī)制為動(dòng)態(tài)再結(jié)晶，其在400℃時(shí)塑性最好，2024鋁合金主要軟化機(jī)制為動(dòng)態(tài)回復(fù)，無塑性最高點(diǎn)。 對(duì)于壓縮變形，同樣建立了熱變形本構(gòu)方程，基于動(dòng)態(tài)材料模型（DMM）和Prasad的失穩(wěn)準(zhǔn)則，給出了不同形變參數(shù)下的應(yīng)變速率敏感指數(shù)(m)、能量消耗效率(η)及流變失穩(wěn)區(qū)域，并最終繪制出熱加工圖。結(jié)合熱加工圖及金相照片得出了合適的合金加工工藝，同時(shí)對(duì)試樣內(nèi)部由于應(yīng)變分布不一而引起的組織不均勻性進(jìn)行了分析。結(jié)果表明：7050鋁合金在400℃低應(yīng)變速率下發(fā)生動(dòng)態(tài)再結(jié)晶，適合熱加工。2024鋁合金在250~300℃，低應(yīng)變速率下存在流變失穩(wěn)區(qū)，不適合加工；400℃以上出現(xiàn)能量耗散效率η的峰值，適合進(jìn)行熱加工，軟化機(jī)制以動(dòng)態(tài)回復(fù)為主。
[Abstract]:7000 series and 2000 series aluminum alloy are both high-strength aluminum alloys, widely used in aerospace field, they are known as non-weldable metals. Friction stir welding (FSW) fundamentally solves the problem of high strength aluminum alloy welding. The welding temperature and the plastic flow of metal are very important to weld forming in the actual welding process. Therefore, the study on the hot deformation behavior of the two alloys is of great significance to clarify the welding mechanism and welding process optimization. In this paper, the thermal deformation behavior of 7050 and 2024 aluminum alloys has been systematically studied by means of physical simulation and Gleeble-3500 thermal simulator using tensile and compression methods, respectively. From the point of view of rheological stress, the changes of the two alloys are similar, and are significantly affected by strain rate and temperature. As a whole, the flow stress decreases with the increase of temperature and the decrease of strain rate. For tensile deformation, the effects of temperature and strain rate on metal plasticity were discussed, and the constitutive equation of thermal deformation was established. The results show that the plasticity of the two alloys increases with the increase of deformation temperature and the decrease of strain rate. Compared with 2024 aluminum alloy, the hot deformation activation energy Q is smaller, which indicates that the former is more prone to dynamic recrystallization. Dynamic recrystallization is the main softening mechanism of 7050 aluminum alloy under the experimental conditions, and the main softening mechanism of 2024 aluminum alloy is dynamic recovery at 400 鈩

本文編號(hào)：2128316