6061鋁合金半固態變形特性及顯微組織變化之研究

Abstract

半固態成形技術可以改善以往鍛造有殘留應力及鑄造有氣孔、夾渣的缺點，製造出無孔洞的成品、排除殘留應力、且成形速度快以及能得到更好的機械性質。此技術主要可以分為兩個階段實施，第一階段是準備半固態成形用胚料，第二階段是將胚料升溫至半固態下進行成形加工。 本實驗是使用大量塑性變形法中的等徑轉角擠製法來製作半固態成形用胚料，使胚料產生超細晶粒且升溫至半固態下能具有球狀晶的結構。 本研究主要探討在半固態溫度下6061鋁合金的變形特性及顯微組織變化情形，利用高週波感應加熱設備對試片進行升溫及持溫，觀察試片在半固態持溫時顯微組織的變化，以及利用壓縮試驗，比較原素材及經等徑轉角擠製之試片其成形性的差異。 實驗結果顯示晶粒尺寸及形狀因子皆對壓縮結果是有較大的影響。較小的晶粒尺寸及較佳的形狀因子能讓試片在壓縮過程中固液相呈現均勻的分佈，可以有效地保持試片壓縮時的完整性，且成形負荷低，是有利於半固態成形的。

The technique of Semi-Solid Metal Forming can decrease residual stress during forging and avoid producing products with air pockets and slag in casting. Semi-Solid Metal Forming further reduces the cost in forming time and ensures better mechanical properties. This process is divided into two stages. The first stage is to prepare the billets for forming. In the second stage, the billets are heated to the semi-solid state and then proceed to forming process. The experimental method, Equal Channel Angular Extrusion, is adopted to produce the billets. By conducting this method, billets produce ultrafine-grain and spherical grains in the semi-solid state. In this study, the deformation behavior and the variations of microstructures of 6061 Aluminum Alloy in the semi-solid state were discussed. Changes of microstructures were observed by heating and isothermal holding by the High Frequency Induction Heating System. Also, we compared the differences in formability between Al-6061 Alloy and ECAE Al-6061 Alloy by compression tests. The result indicated that grain size and shape factor have significant effect on the compression results. The solid-liquid state was found in a uniform distribution found from smaller grain size and better shape factor. This has benefit on maintaining the integrity of billets and decreasing the load during the compression. Therefore, grain size and shape factor are beneficial to semi-solid forming.