Mg-4Al-2Si合金固溶处理过程中Mg_2Si相颗粒的球状化

实验研究了Mg-4Al-2Si合金固溶处理过程中汉字状Mg2Si相颗粒的球化现象及其工艺参数对球化的影响。结果发现:Si沿Mg/Mg2Si界面扩散,使粗大的汉字状Mg2Si颗粒发生部分溶断,并依靠自发球化的趋势通过向未溶的粒状Mg2Si扩散聚集完成球化;最佳球化工艺为420℃保温16h。

Influence of solution treatment on microstructure and properties of in-situ Mg_2Si/AZ91D composites

The influence of solution treatment on the microstructure and properties of Mg2Si/AZ91D composites fabricated from Mg-SiO2 system via in-situ processing method was investigated.The results show that coarse Chinese script shape Mg2Si phases can be formed by adding SiO2 into AZ91D magnesium alloy with Si content up to 1.5% of the alloy melt.During solution treatment,the morphology and distribution of the coarse Chinese script shape Mg2Si phases are modified.Meanwhile,the β-Mg17Al12 phase is dissolved into the magnesium matrix.With increasing holding time,the coarse Mg2Si phases tend to dissolve,break and spheroidize.After solution treatment at 420 ℃ for 16 h,Mg2Si phases become the finest and relatively well-distributed phase.The tensile strength and elongation are increased by 14.9% and 38.9%,respectively.It is believed that the Mg2Si phases continuously dissolve and break,and finally the spheroidized Mg2Si particles are obtained due to the interface tension of Mg2Si/Mg interface.

Effect of cooling rates on as-cast microstructures of Mg-9Al-xSi(x=1,3) alloys

The effects of cooling rates corresponding to different diameters of the steel mould and laser surface melting(LSM)on the as-cast microstructures of Mg-9Al-xSi(x=1,3)(mass fraction,%)alloys were investigated by XRD and OM.The results show that obvious refinement of the alloy microstructure is obtained with increasing cooling rate by conventional ingot metallurgy.However, no evident modified morphologies of both dendritic primary Mg2Si and Chinese script eutectic Mg2Si in the Mg-Al-Si alloy occurs. Surprisingly,the morphologies of Mg2Si phases within the laser-melted Mg-Al-Si alloy transform drastically from both coarse Chinese script shape for the eutectic Mg2Si and dendrite for the primary Mg2Si to fine spherical particles with an average size of about 3μm due to the rapid cooling of the melted layer,and the Mg2Si particulates distribute more uniformly in theα-Mg matrix.

固溶处理对SiC_p增强AZ91D镁合金组织及硬度的影响

采用不同固溶温度及保温时间,研究了SiC p增强AZ91D镁合金组织演变及硬度变化行为。结果表明,随固溶温度提高,铸态组织中连续网状β相逐渐消失,汉字状Mg2Si相发生熔断,球化速度加快,400℃时晶界清晰。400℃×16h固溶时,不稳定β相几乎完全固溶至基体中,汉字状Mg2Si球化效果最佳,Al8Mn5相未发生明显变化。400℃×20h固溶后,Mg2Si球化趋势开始减弱,晶粒尺寸出现显著增加。结果表明,β相的消失和Mg2Si相的球化导致合金硬度发生连续下降。400℃×16h后由于固溶强化效果的增加,合金硬度有所提高。