(1. 蘭州理工大學 甘肅省有色金屬新材料省部共建國家重點實驗室，蘭州 730050；
2. 蘭州理工大學 有色金屬合金反加工教育部重點實驗室，蘭州 730050)
摘 要: AZ91D鎂合金經(jīng)重熔加入0.3%(質量分數(shù))SiC細化后澆注成不同尺寸(直徑)的錠料。研究SiC對不同尺寸AZ91D鎂合金坯料半固態(tài)等溫熱處理組織的影響。結果表明：未經(jīng)SiC細化處理AZ91D鎂合金的半固態(tài)組織存在明顯的尺寸效應，從心部到邊緣，固相顆粒尺寸由大逐漸變小，如d 70 mm試樣內的固相顆粒尺寸從心部的150 μm變?yōu)檫吘壍?10 μm，并趨于圓整，液相逐漸增多；隨著坯料尺寸的增加，由心部到邊緣的組織差異進一步加大。SiC細化的AZ91D鎂合金坯料經(jīng)半固態(tài)等溫熱處理后，其組織中的固相顆粒尺寸整體變得細小，d 70 mm試樣內的固相顆粒均不大于80 μm，邊緣和心部的固相顆粒尺寸變得很相近，在70 μm與80 μm之間，球化圓整且分布均勻；經(jīng)SiC處理的半固態(tài)壓鑄件中，氣孔等缺陷明顯減少。
關鍵字: 鎂合金；SiC顆粒；半固態(tài)等溫熱處理；尺寸效應；晶粒細化
（1. State Key Laboratory of Gansu Advanced Non-ferrous Metal Materials,
Lanzhou University of Technology, Lanzhou 730050, China;
2. Key Laboratory of Non-ferrous Metal Alloys and Processing, Ministry of Education,
Lanzhou University of Technology, Lanzhou 730050, China）
Abstract:AZ91D magnesium alloy was remelted; then, 0.3%(mass fraction) SiC particles as grain refiner were introduced into the melt; and finally, the melt was poured into cavities with different diameters to form ingots. Those ingots were cut into some billets with determined diameters, and heated to semisolid temperature. The effect of SiC addition on microstructure of mutative-size AZ91D initial billet during semisolid isothermal heat treatment was studied. The results show that there is an obvious dimensional effect on microstructure for semi-solid AZ91D alloy without SiC. In other words, the microstructures from center to edge for the AZ91D billet are different. The size of solid particles gradually changes from large to small. For example, the size of solid particles of the billet with d70 mm changes from 150 μm to 110 μm, and the particles tend to be gradually spheroid and more liquid. With increasing diameter of the billet, the difference of microstructures from center to edge for the billet further increases. For AZ91D alloy with SiC addition, the average size of solid particles becomes smaller than that without SiC addition after isothermal treatment. The size of solid particles of the billet with d 70 mm is not larger than 80 μm. And the solid particle sizes of the billet with SiC from edge and center areas are almost of identical dimension, between 70 μm and 80 μm and in spheroid shape with homogeneous distribution. Casting defects for AZ91D alloy with SiC addition, such as porosity, decrease significantly after SiC semisolid die-casting.
Key words: magnesium alloy; SiC particle; semisolid isothermal heat treatment; dimensional effect; grain refinement
