不同搅拌条件下过共晶Al-Mg-Si熔体中原位结晶强化相的析出行为

Precipitation Behavior of Reinforced Phases in In-situ Crystallization of Hypereutectic Al-Mg-Si Melt Under Stirring Conditions

选用纯铝、结晶硅、Al-50%Mg中间合金配制过共晶Al-Mg-Si熔体,熔体在无搅拌、电磁搅拌2种条件下在石墨模具中铸态成型。Mg2Si相在凝固过程中原位析出为铝基体的颗粒强化相,其理论质量分数为20%,制得Mg2Si颗粒增强铝基原位复合材料。金相和SEM检测结果显示,无搅拌试样中初晶Mg2Si尺寸20-40μm,呈块状,在基体中分布弥散均匀;共晶Mg2Si呈枝杈状;搅拌试样中块状初晶Mg2Si尺寸增大,并呈明显的“中心少、边缘多”的偏析,具有表面强化的效果,共晶Mg2Si呈手指纹状。结果认为,无论是初晶还是共晶Mg2Si相都会受到凝固条件的影响。如果要制备均质Al-Mg2Si复合材料,宜选用铸态;如果要制备表面强化的Al-Mg2Si复合材料,宜选用适当强度的电磁搅拌成型。

Pure aluminum, crystallized silicon and Al-50wt. % Mg interalloy are utilized to synthesize hypereutectic AlMgSi melt. The melt is cast in graphite mold without and with electromagnetic stirring （EMS）. The Mg2Si phase, which acted as reinforced phase, were precipitated from the insitu composites during solidification. So aluminum matrix composites reinforced by 20wt. % Mg2Si were in situ fabricated. The metallographic and SEM analysis showed that, in the sample without EMS, the primary Mg2Si revealed block-like with sizes of 20 - 40 μm. The particles were well distributed in the matrix. While eutectic Mg2Si showed branch-like in shape. However, the size of primary Mg2Si in the sample with EMS increased. The amount of Mg2Si at edge is larger than that in the inner part, which acts as surface reinforced phase. And eutectic Mg2Si shows dectylogram-like. Both the primary and eutectic Mg2 Si depend on the solidification condition. The Al-Mg2 Si composites with uniformly distributed Mg2 Si can be obtained under as-cast condition, while the Al-Mg2Si surface reinforced composites can be prepared by medium intensity electromagnetic stirring.