Mechanical and metallurgical properties of friction stir welded dissimilar joints of AZ91 magnesium alloy and AA 6082-T6 aluminium alloy

In the present research work,AZ91 magnesium alloy and AA6082-T6 aluminium alloy were joined by friction stir welding process.The comparison of microstructure and mechanical properties between different joints by varying the different materials on advance and retreating sides were mainly studied.Four different welds have been prepared to find the material mixing between the similar and dissimilar joints.The joint interfaces of the welds have been investigated by employing an optical microscope and scanning electron microscope.When Mg was placed on advancing side(AS),more aluminium content was soluble in nugget zone than the case where Mg was placed on the retreating side(RS).Thin intermetallic layer in the joint interface of Mg/Al and thick intermetallic layer with poor adhesion of the aluminium and magnesium have been observed in the dissimilar joints varying the sides.The highest UTS of 172.3 MPa was found for Mg-Al when Mg was placed on AS and lower UTS of 156.25 MPa was obtained when Mg was placed on RS.Hardness of 86 Hv and 89 Hv were observed in the Stir zone for the dissimilar AZ91 Mg alloy and AA6082-T6 Al alloy when AZ91Mg alloy was placed on the AS and on the RS respectively.Fractography was also carried out to find the mode of failure.

激光表面熔化对SiC和MoS2颗粒增强Al-4.5Cu复合材料表面完整性的影响（英文）

以Al-4.5Cu合金为基体,用搅拌铸造法制备两种复合材料。一种是用10%SiC(质量分数)和2%MoS2(质量分数)进行增强,另一种是用10%SiC(质量分数)和4%MoS2(质量分数)进行增强。为了研究激光表面熔化(LSM)对材料表面性能的影响,采用CO2激光束对材料表面进行重熔。研究激光熔化表面的形貌、显微硬度、耐蚀性和耐磨性。将LSM后的整体表面完整性与铸态表面进行比较。结果表明,LSM能提高每种情况下表面的显微硬度和耐磨性。激光熔化表面孔隙率低,耐蚀性高。因此,LSM可以方便地应用于提高铝基复合材料的表面完整性。然而,在本研究中存在一个最佳的激光比能以获得最佳的表面完整性,约为38 J/m^2。

Optimization of green sand mould system using Taguchi based grey relational analysis

The strength of the mould cavity in sand casting is very much significant to attain high-quality castings. Optimization of green sand process parameters plays a vital role in minimizing casting defects. In the present research work, the effect of process parameters such as AFS grain fineness number, water, molasses, bentonite, fly ash, and ramming, and their levels on the resultant mould properties were investigated and optimized using Taguchi based grey relational analysis. The Taguchi L18 orthogonal array and analysis of variance(ANOVA) were used. The quality characteristics viz., green compression strength, permeability, bulk density, mould hardness and shatter index of green sand mould were optimized using grey relational grade, based on the experiments designed using Taguchi's Design of Experiments. ANOVA analysis indicated that water content is the most influential parameter followed by bentonite, and degree of ramming that contributes to the quality characteristics. The results are confirmed by calculating confidence intervals, which lies within the interval limits. Finally, microstructure observations and X-ray diffraction analysis have been performed for the optimal sand parametric combination. Results show that presence of maximum amount of SiO_2, which might be the reason for enhancement of the physical properties of the sand.

搅拌铸造竹叶灰铝基复合材料的显微组织和力学性能（英文）

以从农业废物中分离出的竹叶灰(BLA)为增强剂,当竹叶灰(BLA)含量分别为2%、4%和6%时,以Al-4.5%Cu合金为基体,采用搅拌铸造方法制备复合材料。该复合材料由于基体和增强粒子之间的有效结合,而具有优越的性能。采用各种试验确定该复合材料的力学性能,如密度、孔隙度、硬度和抗拉强度。将所得结果与基体合金相进行比较。采用OM、SEM-EDAX和XRD分析方法对所选基体合金中增强粒子的分散性进行分析。结果表明,复合材料中BLA颗粒均匀分布于晶体内。此外,还观察到BLA颗粒与基体合金有良好的结合,且界面清晰。随着BLA颗粒质量分数的增加,复合材料的密度降低,而孔隙度增大。当复合材料中BLA颗粒含量达到4%时,材料的硬度和抗拉强度都增加,而当BLA含量进一步增加时,硬度和抗拉强度都会降低。

晶粒细化和残余元素对A713铸态铝合金热裂行为的影响（英文）

为减少或防止热裂现象的产生,研究具有长程凝固区A713铸态铝合金的热裂行为。对添加不同晶粒细化剂如Al-2.5Ti-0.5C和Al-3.5Ti-1.5C的合金在不同浇铸温度(700、750和780°C)条件下进行热裂实验。结果表明:添加晶粒细化剂Al-3.5Ti-1.5C能减少热裂现象的产生,但仅添加晶粒细化剂不能完全阻止A713铸态铝合金中热裂现象的产生。这与早期一些研究者得出的结论相矛盾。考察了铁元素对A713铸态铝合金热裂行为的影响。结果显示,同时添加晶粒细化剂和铁元素能减少A713铝合金的内部枝晶分离,从而沿晶界产生枝晶间的联锁。因此,铁元素作为工业铝中的一种杂质元素,能阻止A713铝合金热裂现象的产生。

Grain refinement of Al-3.5FeNb-1.5C master alloy on pure Al and Al-9.8Si-3.4Cu alloy

The refinement potential of Al-3.5 Fe Nb-1.5 C master alloy on pure aluminium and Al-9.8 Si-3.4 Cu alloy has been investigated. Different amounts of Al-3.5 Fe Nb-1.5 C master alloy were added to estimate the optimal addition level. It was found that the addition of Al-3.5 Fe Nb-1.5 C grain refiner can promote significantly the refinement of grains in the pure aluminium, particularly at 0.1 wt.%, with the mean primary aluminium α-grain size reducing to 187±3 μm from about 1-3 mm. Similarly, the microstructural study of the Al-9.8 Si-3.4 Cu alloy die casting at different weight percentages(viz. 0.0 wt.%, 0.1 wt.% and 1.0 wt.%) of Al-3.5 Fe Nb-1.5 C master alloy shows that the Al-3.5 Fe Nb-1.5 C master alloy as a grain refiner is also acceptable for Al-Si cast alloys when the silicon content is more than 4 wt.%. As a result of inoculation with Al-3.5 Fe Nb-1.5 C master alloy, the average grain size of α-Al is reduced to 22±3 μm from about 71±3 μm and grain refining efficiency is not characterized by any visible poisoning effect, which is the major limitation in the grain refinement of Al-Si cast alloys by applying Al-Ti-B ternary master alloys. Mechanical properties such as ultimate tensile strength and yield strength are significantly improved by 9.6% and 9.7%, respectively.

基于QFD-Taguchi混合方法的型模铸造工艺优化（英文）

采用基于QFD-Taguchi的混合方法对高温型模铸造的多种重要工艺参数进行确认和优化,以便获得A380合金最适宜的铸造密度。为研究型模铸造工艺的性能特征,首先确认关键工艺参数,选择合适的正交序列,然后进行均差和方差分析。通过基于QFD-Taguchi的混合方法确认和优化了型模铸造的工艺参数,并将之应用于实验中。结果表明,在所选参数中,注射压力是最重要的参数。注射压力对平均铸造密度变化的贡献约为61.483%。95%一致性水平的置信区间约为0.000718,验证了A380合金优化铸造密度的预估区间。