In situ fabrication and properties of Al N dispersion strengthened 2024 aluminum alloy

Nanoscaled aluminum nitride （AlN） dispersion strengthened 2024 aluminum alloy was fabricated using a novel approach in which Al-Mg-Cu compacts were partially nitrided in flowing nitrogen gas. The compacts were subsequently consolidated by sintering and hot extrusion. The microstructure and mechanical properties of the material were preliminarily investigated. Transmission electron microscopy and X-ray diffraction results revealed that AlN particles were generated by the nitridation of Al-Mg-Cu compacts. The material exhibited excellent mechanical properties after hot extrusion and heat treatment. The ultimate tensile and yield strengths of the extruded samples containing 8.92vol% AlN with the T6 heat treatment were 675 and 573 MPa, respectively.

Effect of large cold deformation after solution treatment on precipitation characteristic and deformation strengthening of 2024 and 7A04 aluminum alloys

The effects of large cold deformation after solution treatment on the precipitation characteristic and deformation strength of 2024 and 7A04 Al alloys were investigated.The tensile property tests indicate that the ageing response of the 2024 aluminum alloy is accelerated when treated by cold deformation after solution treatment,and the tensile strength is increased to about 140 MPa while the elongation still keeps above 8%.However,compared with the 2024 alloys,although the aging response of the cold deformed 7A04 aluminum alloy is accelerated,the tensile strength has not changed obviously and the elongation is even decreased drastically.The results of TEM observation show that the S’ phase inside the dislocation cells and at the boundaries of the dislocation cells of the 2024 aluminum alloy has a uniform distribution.But in 7A04 aluminum alloy the club-shaped η’ phase forms at the boundaries of dislocation cells even on dislocation lines,while there still exists small spheric G.P zone in the region with less dislocation.In addition the precipitates in 7A04 alloy with cold rolling present more obvious tendency of growth and coarsening than those without cold rolling.It is indicated that the coherent strain energy of the cylinder formed G.P zones with matrix in the 2024 alloy is smaller than that of the spherical G.P zone in 7A04 alloy,for which a different distribution of precipitates and different effect of strengthening are caused in artificial ageing after resolution treatment and large cold deformation.

Effect of large cold deformation on characteristics of age-strengthening of 2024 aluminum alloys

Effect of large cold deformation on the age-hardening characteristics of 2024 aluminum alloys was investigated. The results reveal: 1) the aging response is accelerated after large cold deformation, and the peak strength is attained after aging for 40 min; 2) double aging peaks can be found in the age-hardening curves, and the first peak appears when aged for 40 min. The corresponding peak tensile strength (sb) and elongation are up to 580 MPa and 9.2% respectively, the second peak appears when aged for 120 min, but the peak tensile strength(520 MPa) is lower than the first one; 3) in early stage of aging (<40 min), elongation slightly increases from 8% with prolonging aging time of the alloy. Elongation markedly decreases to 2% after aging for 60 min, and shows a plateau with the prolonging of aging time on the age-elongation curve. It is indicated that the high density of dislocation introduced by large deformation accelerates the precipitation of GP zones and the aging response of the alloy. The first aging peak is due to the formation of GP zones and the deformation strengthening caused by the high density of dislocation. And the second peak present in the aging curve is attributed to the nucleation and growth of S’ phase. The offset between dislocation density decreases and precipitation S’-phase finally results in the phenomenon of double aging peaks when aged at 190 ℃. Moreover, it is suggested that the formation of PFZ and coarse equilibrium phase accompanied by the precipitation of S’ phase decrease the elongation.

Strengthening technology and mechanism for semi-solid die casting of aluminum alloy

Combined with theoretical evaluation, an optimized strengthening process for the semi-solid die castings of A356 aluminum alloy was obtained by studying the mechanical properties of castings solution treated and aged under different conditions in detail, then, the semi-solid die castings and liquid die castings were heat treated with the optimized process. The results show that the mechanical properties of semi-solid die castings of aluminum alloy are superior to those of the liquid die castings, especially the strengthening degree of heat treated semi-solid die castings is much greater than that of liquid die castings with the tensile strength more than 330 MPa and the elongation more than 10%, and this is mainly contributed to the non-dendritic and more compact microstructure of semi-solid die castings. The strengthening mechanism of heat treatment for the semi-solid die castings of A356 aluminum alloy is due to the dispersive precipitation of the second phase（Mg2Si） and formation of GP Zone.

Effect of minor Sc and Zr addition on microstructure and properties of ultra-high strength aluminum alloy

The Al-9Zn-2.8Mg-2.5Cu-xZr-ySc alloys （x=0, 0.15%, 0.15%; y=0, 0.05%, 0.15%）, produced by low-frequent electromagnetic casting technology, were subjected to homogenization treatment, hot extrusion, solution and aging treatment. The effects of minor Sc and Zr addition on microstructure, recrystallization and properties of alloys were studied by optical microscopy （OM）, scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The results show that Sc and Zr addition can refine grains of the as-cast alloy by precipitation of primary Al3（Sc,Zr） particles formed during solidification as heterogeneous nuclei. Secondary Al3（Sc,Zr） precipitates formed during homogenization treatment strongly pin the movement of dislocation and subgrain boundaries, which can effectively inhibit the alloys recrystallization. Compared with the alloy without Sc and Zr addition, the Al-Zn-Mg-Cu-Zr alloy with 0.05%Sc and 0.15%Zr shows the increase in tensile strength and yield strength by 172 MPa and 218 MPa, respectively. Strengthening comes from the contributions of precipitation, substructure and grain refining.

Time-temperature-property curves for quench sensitivity of 6063 aluminum alloy

The quench sensitivity of 6063 alloy was investigated via constructing time-temperature-property（TTP） curves by interrupted quenching technique and transmission electron microscopy（TEM） analysis.The results show that the quench sensitivity of 6063 alloy is lower than that of 6061 or 6082 alloy,and the critical temperature ranges from 300 to 410℃ with the nose temperature of about 360℃.From TEM analysis,heterogeneous precipitate β-Mg2Si is prior to nucleate on the（AlxFeySiz） dispersoids in the critical temperature range,and grows up most rapidly at the nose temperature of 360℃.The heterogeneous precipitation leads to a low concentration of solute,which consequently reduces the amount of the strengthening phase β＇＇ after aging.In the large-scale industrial production of 6063 alloy,the cooling rate during quenching should be enhanced as high as possible in the quenching sensitive temperature range（410-300℃） to suppress the heterogeneous precipitation to get optimal mechanical properties,and it should be slowed down properly from the solution temperature to 410℃ and below 300℃ to reduce the residual stress.

Aging behavior and mechanical properties of 6013 aluminum alloy processed by severe plastic deformation

Structural features, aging behavior, precipitation kinetics and mechanical properties of a 6013 Al–Mg–Si aluminum alloy subjected to equal channel angular pressing （ECAP） at different temperatures were comparatively investigated with that in conventional static aging by quantitative X-ray diffraction （XRD） measurements, differential scanning calorimetry （DSC） and tensile tests. Average grain sizes measured by XRD are in the range of 66-112 nm while the average dislocation density is in the range of 1.20×10^14-1.70×10^14 m^-2 in the deformed alloy. The DSC analysis reveals that the precipitation kinetics in the deformed alloy is much faster as compared with the peak-aged sample due to the smaller grains and higher dislocation density developed after ECAP. Both the yield strength （YS） and ultimate tensile strength （UTS） are dramatically increased in all the ECAP samples as compared with the undeformed counterparts. The maximum strength appears in the samples ECAP treated at room temperature and the maximum YS is about 1.6 times that of the statically peak-aged sample. The very high strength in the ECAP alloy is suggested to be related to the grain size strengthening and dislocation strengthening, as well as the precipitation strengthening contributing from the dynamic precipitation during ECAP.

Structure and properties of an ultra-high strength 7xxx aluminum alloy contained Sc and Zr

An ultra-high strength aluminum alloy was produced by casting and then extruded to rods. The effect of heat treatment on the microstructure and mechanical properties of the alloy was investigated. After single ageing （120℃, 24 h）, the tensile strength was 812.4 MPa and the elongation was 6.2%. After retrogression reaging （RRA）, the tensile strength was 751.2 MPa and the elongation was 6.4%. The strengthening mechanism is considered as fine grain strengthening, substructure strengthening and dispersion strengthening by Al3（Sc, Zr）.

Effect of magnesium on dispersoid strengthening of Al-Mn-Mg-Si(3xxx) alloys

The effects of magnesium addition on the dispersoid precipitation as well as mechanical properties of 3xxx alloys wereinvestigated. The microstructures in as-cast and heat-treated conditions were evaluated by optical microscopy and transmissionelectron microscopy. The results reveal that Mg has a strong influence on the distribution and volume fraction of dispersoids duringprecipitation heat treatment. The microhardness and yield strength at ambient temperature increase with increasing Mg content. Thesolid solution and dispersoid strengthening mechanisms of materials after heat treatment are quantitatively analyzed. Dispersoidstrengthening for the alloys is the predominant strengthening mechanism after precipitation heat treatment. An analytical model isintroduced to predict the evolution of ambient-temperature yield strength.

Co-strengthening contribution of δ′and T_1 precipitates in Al-Li alloys 2090 and 2090+Ce

The microstructure of dislocation in two kinds of ahiminum-lithium alloys 2090 and 2090 ＋ Ce was observed by means of TEM technology. The contributions of δ＇ and T1 precipitates to strength were separately calculated by using the results of quantitative metallography and analysis of micro-deformation behavior; the co-strengthening effect of δ＇ and T1 precipitates was studied. The results show that the adding relationship of co-strengthening of δ＇ and T1 is in accordance with q = 1.4 form at the near peak-aged condition, i.e., △τ^1.4δ = △τ^1.4δ＋ △τ^1.4T1, but the adding relationship is approximately a linear relation （q = 1） at the under-aged condition and becomes the parabola form when over-aged （q = 2）. The adding relationship of co-strengthening contribution of δ＇ and T1 is obviously dependent on aging time.

Strength and ductility optimization of HPDC AlSi8MgCuZn2 alloys by modifying pre-aging treatment

Considering the components produced by high pressure die casting(HPDC)process usually with ultra-large sizes and complex morphologies,high temperature solid solution treatment is not a suitable method to further improve their mechanical properties.In this study,two-stage aging treatment with different pre-aging times was designed and employed to further improve the mechanical properties of HPDC Al8SiMgCuZn alloy.The characteristics of precipitates were evaluated by a transmission electron microscope(TEM),and the precipitation strengthening mechanism was discussed.The results reveal that the strengthening is mainly contributed by the precipitation ofβ″phase after two-stage aging,and the number density and size of the precipitates are significantly depended on the pre-aging time.The number density of precipitates is increased with the pre-aging time prolonged from 0 h to 4 h,and then decreases with the further increase of pre-aging time from 4 h to 6 h.The precipitates with the highest density and smallest size are observed after pre-aging for 4 h.After pre-aged at 100℃for 4 h and then artificial aged at 200℃for 30 min,the yield strength of 207 MPa,ultimate tensile strength of 325 MPa and elongation of 7.6%are achieved.

Influence of pre-stretching on quench sensitive effect of high-strength Al-Zn-Mg-Cu-Zr alloy sheet

The influence of pre-stretching on quench sensitive effect of high strength Al-Zn-Mg-Cu-Zr alloy AA 7085 sheet was investigated by tensile testing at room temperature,transmission electron microscopy(TEM)and differential scanning calorimetry(DSC).The water-cooled and aged alloy exhibits higher strength than the air-cooled and aged alloy;2.5%pre-stretching of tensile deformation exerts little effect on strength of water-cooled and aged alloy but increases that of air-cooled and aged one,and therefore the yield strength reduction rate due to slow quenching decreases from about 3.8%to about 1.0%,reducing quench sensitive effect.For the air-cooled alloy,pre-stretching increases the sizes ofη'strengthening precipitates but also increases their quantity and the ratio of diameter to thickness,resulting in enhanced strengthening and higher strength after aging.The reason has been discussed based on microstructure examination by TEM and DSC.

MICROSTRUCTURE AND DECOMPOSITION OF RS Al-Fe-Cr-Zr ALLOY

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粘铝合金板加固RC梁抗弯性能试验及正截面承载力

为了探讨铝合金板厚度与端部U形铝合金箍板构造对RC梁破坏机理及抗弯性能的影响,对16根铝合金板加固RC梁进行了4点弯曲静力加载试验。在试验梁底铝合金板的表面以及试验梁跨中截面的顶面、侧面粘贴应变片,在试验梁底跨中、梁顶两端支座布置百分表。为了推导铝合金板加固RC梁的正截面承载力计算式,基于试验得到的破坏机理,通过引入6个基本假定,分析了5种不同破坏模式的相对受压区高度。建立了各破坏模式下铝合金板加固RC梁的正截面承载力计算式,并将其与引入文献中的试验结果进行了对比分析。结果表明:试件破坏形态包括适筋破坏、端部铝合金板与结构胶剥离、端部铝合金板与梁剥离及中部铝合金板剥离4种情况;当端部设置U形铝合金箍板时,可有效抑制端部铝合金板发生剥离,使钢筋与铝合金板的材料性能得到充分发挥,试件承载力与延性明显提升;当铝合金板厚度分别为2~6 mm时,试件承载力随铝合金板厚度的增加而提高;端部设置U形铝合金箍板可有效防止端部铝合金板发生剥离,但试件仍可能会出现中部铝合金板剥离现象;当试件出现适筋破坏特征时,试件抗弯承载力的计算值与试验值比值均在1以下。本研究所提计算式具有明显的规律性和适用性,可为工程实际设计提供参考。

基于电接触强化的铝合金表面电刷镀镍层改性研究

[目的]对铝合金进行表面处理可提高其硬度和耐磨性,拓宽铝合金材料在机械零件方面的应用。[方法]采用电刷镀技术在1060铝合金表面制备Ni镀层,再通过电接触强化技术对Ni镀层进行改性。采用扫描电子显微镜和维氏硬度计考察了Ni镀层电接触强化前后的微观组织和显微硬度。通过摩擦磨损试验对比了1016铝合金及Ni镀层电接触强化前后的耐磨性。[结果]经电接触强化后,Ni镀层内部的裂纹及孔洞类缺陷减少,晶粒间隙减小,致密性提高,显微硬度增大到524.4~560.3 HV0.1范围内。1016铝合金在摩擦磨损试验后存在较深的犁沟和剥落,耐磨性较差。Ni镀层的耐磨性优于1016铝合金,但在摩擦过程中会发生剥落。经电接触强化的Ni镀层在摩擦过程中摩擦因数平稳,表面只是轻微擦伤,耐磨性最佳。[结论]结合电刷镀镍和电接触强化技术可显著提高铝合金的表面性能。

Zr对Al-Si-Mg-Mn合金凝固过程、时效组织和性能的影响

通过模拟计算、组织观察以及力学性能测试,研究了不同Zr含量对铸造Al-Si-Mg-Mn合金凝固过程、时效组织及力学性能的影响。结果表明,随着Zr含量增加,合金凝固路径存在显著差异,晶粒由初期树枝晶逐步演变为等轴晶;175℃时效7 h条件下,Zr的加入显著提高合金硬度。Zr的加入促使析出相在更低时效温度析出,这可能是Zr细化了晶粒从而提高了扩散效率。峰值时效时合金主要析出相为β″相和Q′相。

纳米晶Al-xMg铝合金的元素再分布及其对强度的影响

目的针对Al-Mg合金在变形加工过程中容易出现的溶质元素再分布现象,通过微观表征和定量计算深入研究元素再分布的相关机制及其强度贡献。方法利用扫描透射电镜高角环形暗场技术结合几何相位分析,详细研究了溶质元素再分布机理,对经过高压扭转后不同Mg含量的Al-Mg合金中的元素分布进行了表征,并通过原子探针层析技术对原子的三维空间分布情况进行了团簇分析。结果随着Mg的原子数分数从1.0%增加至8.0%,合金硬度从129.0HV显著上升至223.6HV。合金内部的溶质分布状态可以分为溶质原子贫化、溶质原子富集和溶质原子不均匀分布3种,剧烈塑性变形引入的不均匀微观应变诱导了Mg原子的再分布。结论合金中形成的大量原子团簇为Al-8Mg合金贡献了47.7HV的硬度值,占总硬度的21.3%,溶质团簇对合金强度的强化效果十分显著,表明团簇强化是材料强化手段中不可或缺的新型强化机制。

7075铝合金刚柔耦合结构表面疲劳性能探究

采用激光冲击强化技术改善7075铝合金疲劳性能,能够降低成本、提高效率。以7075铝合金为研究对象,通过对其在不同功率密度下的强化试验,测定其在激光冲击下的表面形貌及残余应力的分布情况,结合其疲劳试验,探究激光强化对材料性能的影响。结果表明:激光冲击强化使铝合金表面粗糙度增大,并产生残余压应力;当功率密度增加到10.19 GW/cm^(2)时,残余压应力不再增大;激光冲击试样的疲劳寿命比未冲击试样提高了1倍,减小了断裂扩展范围;残余压应力的存在增加了铝合金的裂纹萌生难度,延长了其疲劳寿命。

喷丸强化覆铝7B04-T7451铝合金的表面完整性及疲劳性能研究

研究了喷丸强化对覆铝7B04-T7451铝合金表面完整性和疲劳性能影响,阐明了覆铝层对喷丸强化效果的影响。采用维氏硬度计、原位纳米测试系统、激光共聚焦显微镜、X射线衍射仪等,分析了喷丸强化后试样的显微硬度、表面轮廓、表面粗糙度及残余应力等的变化。利用疲劳试验机测试喷丸强化试样的疲劳寿命,利用扫描电镜分析疲劳断裂断口的特征。结果表明,喷丸强化覆铝7B04-T7451试样表层硬度从表层向内部逐渐增大,直到基材硬度,表面硬度较原始试样略有提高;覆铝7B04-T7451试样表面发生剧烈的塑性形变,弹丸尺寸较大,表面粗糙度明显增大;喷丸强化引入深度约150μm的残余压应力层,但其残余压应力数值和应力峰值均较小。喷丸强化覆铝7B04-T7451铝合金的疲劳性能没有获得提高,由于表面粗糙度和塑性形变显著增大,使得疲劳裂纹源在覆铝层表面萌生较快,疲劳寿命降低。

预腐蚀条件下不同孔数冷挤压强化7075-T6铝合金板件疲劳寿命退化规律

目的研究腐蚀环境下单孔和多孔冷挤压强化铝合金板件的疲劳寿命退化规律和损伤机理。方法针对2种不同孔距的三孔冷挤压强化7075-T6铝合金板件,采用模拟热带海洋大气环境的实验室加速腐蚀谱,开展不同腐蚀时间下的预腐蚀疲劳试验。结果获得了3倍孔距的三孔挤压强化铝板以及单孔挤压强化铝板的C(t)曲线、疲劳S-N曲线和损伤形貌特征,分析了腐蚀后挤压强化试件的腐蚀机理及挤压强化作用。同时,将不同孔数试件的试验结果进行比较,探明了孔数对挤压强化铝板腐蚀和疲劳性能的影响。结论腐蚀后挤压强化铝合金板件的疲劳性能发生显著退化,腐蚀损伤主要为剥蚀,疲劳裂纹萌生位置由孔边转移至表面。挤压孔数量对挤压强化铝合金板件的疲劳和腐蚀疲劳性能的影响较小。