多道次等通道彎角擠製製程與T6處理 對7075鋁鋅鎂合金機械性質與顯微組織之影響

The Effect of Multi-pass Equal Channel Angular Extrusion Process and T6 Heat Treatment on Microstructures and Mechanical Properties of 7075 Al-Zn-Mg Alloy

徐維駿(Wei-Jun Hsu)

指導教授 ： 曾春風

共同指導教授 ： 郭央諶(Iang-Chuen Kuo)

國立虎尾科技大學/工程學院/材料科學與綠色能源工程研究所/碩士(2014年)

摘要

等通道彎角擠製（Equal Channel Angular Extrusion）是一個使金屬產生剪切應變的製程。ECAE的模具具有彎角且等截面的通道，施加外力使金屬通過此通道以產生均勻的激烈塑性變形，因為金屬在彎角處的流變而產生非常高的壓力，且因橫截面積保持不變，金屬可以被擠壓數多次不斷的累積大量的剪切應變而造成晶粒細化，使金屬可提升強度硬度亦能增加伸長率。
本研究由預備實驗尋找7075鋁合金合適的擠製溫度後，在固定的擠製路徑下進行多道次擠製及T6處理，藉由改變擠製參數(溫度、道次)與製程方法(固溶、淬冷及擠製的順序)，以了解這些參數與製程方法對擠製後材料的機械性質和顯微組織影響；並比較不同製程方法下的優缺點及應變量對再結晶與析出硬化的影響，最後證實經過ECAE製程能優化材料的機械性質。
研究結果發現，退火及固溶狀態7075鋁合金須在最低165oC的擠製溫度，方能順利進行12道次的ECAE製程，並能達到應變硬化的效果。當擠製溫度越低所獲得強化效果越高，擠製溫度越高所獲得伸長率越好，ECAE (165oC或 205oC)製程採用擠製路徑BC，在擠製12道次的試樣皆能獲得最高的伸長率，且使試樣各表面的硬度能達到均勻一致。退火材經165 oC及205 oC-ECAE製程，隨擠製道次增加其硬度及抗拉強度呈現不一致的變化趨勢，但伸長率都一樣在4道次呈現最小值而在12道次達最大值。退火材經165 oC -ECAE製程與T6處理，擠製道次越多獲得峰值硬度的時效持溫時間越短，但硬度值越高；當擠製道次越多所獲得晶粒尺寸越小，12道次試樣晶粒均勻的呈現等軸晶狀，ASTM晶粒尺寸號碼為6。固溶淬冷狀態7075鋁合金經165 oC -ECAE製程與120 oC人工時效時，當擠製道次愈多，獲得峰值硬度的時效持溫時間越短，但硬度越低；反之亦然。固溶材經過165 oC –ECAE擠製2及4道次製程與人工(峰值)時效處理之試樣能大幅提升強度硬度；比固溶材經165 oC -ECAE製程及退火材僅經T6(時效峰值)處理者強化許多且不失延展性。退火材先實施固溶淬冷後經165oC-ECAE製程與人工(峰值)時效處理方法在2道次擠製的強度硬度就與經165oC-ECAE製程與T6(峰值時效)處理方法在12道次擠製的強度硬度達到一樣水準。

關鍵字

等通道彎角擠製 ； 擠製路徑 ； T6處理 ； 擠製參數 ； 擠製道次 ； 晶粒尺寸 ； 人工時效

並列摘要

Equal channel angular extrusion (ECAE) is a shear strain process of metal. ECAE mold has an equal cross-section channel with constant corner angle, an external force is applied to the metal through this channel to produce a homogenous and severe plastic deformation, extruded bulk metal will produce high flow stress due to metal flow at the corner, however the cross-section area of channel remains unchanged, the metal can be extruded continuously to accumulate large shear strain and causes grain refinement result, the hardness and the strength of metal can be increased, and elongation also can be improved.
In this study, the pre-experiment was conducted to find a suitable extruded temperature for 7075 aluminum alloy. The multi-pass extrusion and T6 treatment were carried out at a fixed extrusion route to reveal the effect of extrusion parameters and process methods on mechanical properties and microstructures for extruded aluminum alloy samples by changing these parameters (temperature, passes) and process methods (solid solution treatment, quenching and extruded order); and also to compare the advantages and disadvantages of different process methods. The effect of strain on recrystallization and precipitation hardening was also revealed, and finally we demonstrated that the mechanical properties of the material can be improved through ECAE process.
The experiment results show that annealed and solution-heat-treated 7075 aluminum alloy samples should be extruded at a minimum temperature of 165oC while they can be successfully carried out 12 passes ECAE process, and also achieve the result of strain hardening. The lower is the extrusion temperature, the higher will be the strengthening result obtained; the higher is the extrusion temperature, the better will be the elongation result. The samples which were conducted the ECAE (165oC or 205oC) process using extrusion route BC will obtain the highest elongation in 12 passes extrusion, and surface hardness of each side on extruded samples will achieve uniformity. Annealed samples were extruded by ECAE process at 165 oC and 205 oC, when the extrusion pass increases, both hardness and tensile strength of the samples present different variation tendency; but the elongation of the samples presents a minimum values at 4 passes extrusion and a maximum values at 12 passes extrusion. Annealed sample was extruded by ECAE process at 165 oC and T6 treatment, the higher is the extrusion pass, the shorter will be the aging time which gets peak hardness, but the higher the hardness value. The extruded sample with more extrusion passes gets the smaller grain size, the grains of sample with 12 extrusion passes show uniform equiaxed shape, ASTM grain size number is about 6. While solution-heat-treated 7075 aluminum alloy samples were extruded by ECAE process at 165 oC and subsequently artificially aged at 120 oC, the higher is the extrusion pass, the shorter will be the aging time which gets peak hardness, but the lower the hardness value; and vice versa. The solution-heat-treated samples which were extruded through 2 and 4 passes ECAE process at 165 oC and followed by peak artificial aging treatment can significantly improve the strength and hardness, the increment in strength and hardness for these samples is larger than that of samples which were solution-heat-treated and subsequently ECAE process at 165 oC and annealed then only through T6 (peak aging) treatment, and there is no loss on ductility. The strength and hardness of solution-heat-treated sample which was quenched and followed by 2 passes ECAE process at 165oC and peak artificially aged is almost equal to that of samples which was extruded through 12 passes ECAE process at 165oC and T6(peak artificially aged) treatment.

並列關鍵字

equal channel angular extrusion ； extrusion route, ； T6 treatment ； extrusion parameters ； extrusion pass ； grain size ； artificial aging

參考文獻

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