Effect of microelements on microstructures and properties of Al-1. 2Mg-1. 3Si-0. 6Cu-0. 3Mn alloy

In order to save energy and protect environmentin automobile industry, one of the important methodsis to reduce the automotive weight[1 ～4]. Since the a-luminum alloys showsuch as high specific strength,good formability, good corrosion resistance, and re-cycling potential, they are said to be the ideal candi-date to replace heavier materials in the automotiveindustry[5 ～7].Recently, the heat -treatable 6000series aluminum alloys have been considered as theperfect light-weight material for au…     

Al-3Si-0.6Mg-(Cu,Mn)合金薄板的组织性能

采用拉伸试验、金相、扫描电镜、透射电镜高分辨组织分析方法,研究了水冷铜模铸造的扁锭轧制的Al-3.0Si-0.6Mg-0.4Cu-0.6Mn-0.18Fe合金薄板经400℃至540℃不同温度保温30 min水淬、室温停放90 d(自然时效)后的组织和性能.结果表明:在6009合金基础上提高Si的质量分数至3%,有提高其强度的作用;该合金薄板经540℃×30 min固溶处理自然时效后屈服强度为180 MPa、抗拉强度为313 MPa、延伸率接近23%,其组织中存在Si结晶相及含Fe、Mn和少量Cu、Si的结晶相,以及尺寸小于0.5μm的以含Mn为主并含少量Si和Fe的弥散相;提高其固溶处理温度至540℃,合金薄板的强度明显提高,其原因是析出强化产物尺寸增大,密度提高了.     

合金元素对Al-Si合金力学性能及组织的影响

采用正交试验方法研究Ni、Cr及Zn三种合金元素对Al-7.5Si-3.5Cu-0.35 Mg亚共晶铸造铝硅合金力学性能影响,并用SEM和EDX对加入微量合金后的铸态组织进行观察与分析。结果表明,最优配比为Ni0.02Cr0.03Zn0.2。在合金铸态组织中,Ni、Cr、Zn元素形成复杂的灰白色短棒状或粒状ω相,中和了Fe的有害作用,并且在合金拉伸变形时,可以阻碍位错的运动,对合金基体有一定的强化作用。     

Microstructures and Properties of Al-Zn-Mg-Cu-Zr Alloys with Minor Scandium

The microstructures of Al-Zn-Mg-Cu-Zr al- loys with minor Sc were studied by using optical microscope（OM）, scanning electron microscope （SEM） and transmission electron microscope（TEM）. The tensile mechanical properties and electric conductivity of the studied alloys under different treatment conditions were tested. The results show that adding minor Sc can greatly fines the grain size of the Al-Zn-Mg-Cu-Zr alloy ingots and obviously improves the tensile properties and electric conductivity of the alloys. The strengthening mechanism is considered as fine grain strengthening, sub-structure strengthening and dispersion strengthening by Al3 （Sc, Zr）.     

The effect of Sr and Fe additions on the microstructure and mechanical properties of a direct squeeze cast Al-7Si-0.3Mg alloy

This article describes the results of an investigation into the microstructure and mechanical properties of a gravity die cast and direct squeeze cast LM25 alloy (Al-7Si-0.3Mg-0.3Fe). The direct squeeze cast LM25 alloy has superior mechanical properties compared to the gravity die cast LM25 alloy, especially with regard to ductility, which is increased from ∼1.7 pct for the gravity die cast LM25 alloy to ∼8.0 pct for the direct squeeze cast LM25 alloy in the T6 heat-treated condition. This increase in ductility is due to (1) the removal of porosity, (2) a decrease in Si particle size, and (3) a refinement of the Fe-Si-aluminide particles. High cooling rates in direct squeeze casting result in quench modification of the Si particles, such that chemical modification with Sr or Na may not be required. In addition, direct squeeze casting is more tolerant of Fe impurities in the alloy, due to the formation of smaller Fe-Si-aluminide particles than those in gravity die cast material. The direct squeeze cast LM25+Fe alloy (Al-7Si-0.3Mg-1.0Fe) has a ductility of ∼6.5 pct, compared to that of ∼0.5 pct for the gravity die cast LM25 + Fe alloy in the T6 heat-treated condition. This increase in tolerance to Fe impurities can lead to a substantial reduction in manufacturing costs due to (1) reduced raw-material costs, (2) reduced die sticking, and (3) improved die life.     

Effect of phosphorus modification on the microstructure and mechanical properties of DC cast Al-17.5Si-4.5Cu-1Zn-0.7Mg-0.5Ni alloy

Direct chill (DC) casting of an Al-17.5Si-4.5Cu-1Zn-0.7Mg-0.5Ni alloy with minor additions of Zr, V and Ti was performed and the effect of phosphorus modification on the solidification microstructure and mechanical properties were investigated. The results show that the addition of phosphorus refines the primary Si crystals remarkably but coarsens the eutectic Si in the DC cast billets. In the samples taken in 1/2 radius region of the billets of 100 mm in diameter, the average size of the primary Si particles in the unmodified alloy is 38 μm, while that in the modified alloys range from 13 to 26 μm, depending on the melt treatment time. The AlP particles as heterogeneous nucleation sites for the primary Si crystals were observed in the center of the primary Si particles. In the modified alloy, the achieved ultimate tensile strength is 320MPa and 433MPa respectively in the as-cast state and T6 state. The size of the primary Si particles is critical for the improvement of the mechanical properties of the alloy.     

快速凝固铝锂合金粉末特性对其挤压村组织和性能的影响

采用一种快速冷凝装置研制了Al-2.5Li-1.6Cu-1.2Mg-0.2Zr合金粉末及合金。探讨了合金粉末特性及其对快速凝固铝锂合金微观组织和力学性能的影响。采用片状粉末制备的这种快速凝固铝理合金,具有较好的强塑性综合力学性能。     

Al-2.3Cu-1.7Mg-1.2Fe-1.2Ni合金的时效行为研究

采用硬度测试、电导率测试、常温力学性能测试等方法研究了单级时效处理过程中时效温度和时效时间对Al-2.3Cu-1.7Mg-1.2Fe-1.2Ni合金力学性能和电导率的影响规律,并利用金相显微镜(OM)、扫描电镜(SEM)、透射电镜(TEM)、选区电子衍射(SAED)等手段对合金淬火态以及几种不同时效处理制度下的显微组织进行了研究.结果表明,合金经固溶淬火处理后仍残留有较多的大尺寸第二相,淬火态组织存在的第二相主要有Al9FeNi,Al7 Cu2 Fe,Al7 Cu4 Ni等.单级时效处理过程中,时效处理的温度越高,达到峰时效所需的时间越短,材料的峰时效硬度值越低;电导率随时效时间的延长而不断上升,时效温度越高,电导率的增长速率越快.峰时效条件下合金内主要沉淀强化相包括S’相和S"相,晶界上有明显的链状析出物存在,呈不连续分布;峰时效条件下,合金棒材的极限抗拉强度、屈服强度和延伸率分别为455 MPa,391 MPa和10.6％,电导率可达到21.6 MS·m-1.     

A metallographic study of porosity and fracture behavior in relation to the tensile properties in 319.2 end chill castings

A metallographic study of the porosity and fracture behavior in unidirectionally solidified end chill castings of 319.2 aluminum alloy (Al-6.2 pct Si-3.8 pct Cu-0.5 pct Fe-0.14 pct Mn-0.06 pct Mg-0.073 pct Ti) was carried out using optical microscopy and scanning electron microscopy (SEM) to determine their relationship with the tensile properties. The parameters varied in the production of these castings were the hydrogen (∼0.1 and ∼0.37 mL/100 g Al), modifier (0 and 300 ppm Sr), and grain refiner (0 and 0.02 wt pct Ti) concentrations, as well as the solidification time, which increased with increasing distance from the end chill bottom of the casting, giving dendrite arm spacings (DASs) ranging from ∼15 to ∼95 /im. Image analysis and energy dispersive X-ray (EDX) analysis were employed for quantification of porosity/microstructural constituents and fracture surface analysis (phase identification), respectively. The results showed that the local solidification time(viz. DAS) significantly influences the ductility at low hydrogen levels; at higher levels, however, hydro-gen has a more pronounced effect (porosity related) on the drop in ductility. Porosity is mainly observed in the form of elongated pores along the grain boundaries, with Sr increasing the porosity volume percent and grain refining increasing the probability for pore branching. The beneficial effect of Sr modification, however, improves the alloy ductility. Fracture of the Si, β-Al₅FeSi, α- Al₁₅(Fe,Mn)₃Si₂, and Al₂Cu phases takes place within the phase particles rather than at the particle/Al matrix interface. Sensitivity of tensile properties to DAS allows for the use of the latter as an indicator of the expected properties of the alloy.     

Effect of Combined Addition of Cu and Aluminum Oxide Nanoparticles on Mechanical Properties and Microstructure of Al-7Si-0.3Mg Alloy

In this study, an ultrasonic cavitation based dispersion technique was used to fabricate Al-7Si-0.3Mg alloyed with Cu and reinforced with 1 wt pct Al₂O₃ nanoparticles, in order to investigate their influence on the mechanical properties and microstructures of Al-7Si-0.3Mg alloy. The combined addition of 0.5 pct Cu with 1 pct Al₂O₃ nanoparticles increased the yield strength, tensile strength, and ductility of the as-cast Al-7Si-0.3Mg alloy, mostly due to grain refinement and modification of the eutectic Si and θ-CuAl₂ phases. Moreover, Al-7Si-0.3Mg-0.5Cu-1 pct Al₂O₃ nanocomposites after T6 heat treatment showed a significant enhancement of ductility (increased by 512 pct) and tensile strength (by 22 pct). The significant enhancement of properties is attributed to the suppression of pore formation and modification of eutectic Si phases due to the addition of Al₂O₃ nanoparticles. However, the yield strength of the T6 heat-treated nanocomposites was limited in enhancement due to a reaction between Mg and Al₂O₃ nanoparticles.