Effect of Zn addition on the precipitation behaviors of Al–Mg–Si–Cu alloys for automotive applications

Effect of Zn addition on the precipitation kinetics and age-hardening response of Al–Mg–Si–Cu alloys was investigated by differential scanning calorimetry (DSC), hardness measurements, tensile tests and microstructural characterization. The results show that, compared with the Zn-free alloy, both the starting and peak temperatures in the DSC curve, and activation energy of β″ precipitation of Zn-added Al–Mg–Si–Cu alloy decrease significantly, corresponding to the greatly improved precipitation kinetics and age-hardening response, i.e., a hardness increment of 70HV after aging at 185 °C for 20 min. Moreover, the peak hardness and tensile properties can also be greatly enhanced after adding 3.0 wt% Zn even exhibiting a ductile fracture feature in the peak-aged state. No precipitates of the Al–Zn–Mg alloy system appear in the Zn-added Al–Mg–Si–Cu alloys after aging at 185 °C, and pre-β″, β″, and L precipitates are still the main precipitates in the two alloys after peak aging treatment. Finally, based on the microstructural evolution, a schematic diagram of precipitation in the Al–Mg–Si–Cu–Zn alloy is put forward, and the relationship between mechanical properties and microstructure is also established.     

Effects of grain refinement on age hardening behavior and precipitation kinetics of Al–Si–Cu–Mg alloys

The influences of grain refinement on precipitation kinetics were investigated for an Al–11 wt% Si–1.5 wt% Cu–0.3 wt% Mg casting alloy doped with B and and with La–B respectively by microstructure observation, hardness test and Johnson–Mehl–Avrami (JMA) equation. Co‐alloying of La–B facilitates the faster hardening response with higher hardness value for the alloy. The calculated Avarmi exponent indicates that the nucleation of θ′‐Al₂Cu precipitates occurs on grain boundaries for the refined alloys. The activation energies for the precipitation are of 42 kJ/mol and 30 kJ/mol for B‐doped and La–B co‐doped alloys, respectively.     

Effect of precipitates on properties of cold-rolled Al–Mg–Si–Sc–Zr alloy with higher temperature aging

The aging hardening behaviours of the cold-rolled Al–Mg–Si–Sc–Zr alloy were investigated. The microstructure, hardness and electrical conductivity (EC) of the Al–Mg–Si–Sc–Zr alloy were measured. The relationship between the microstructure and the properties of the Al–Mg–Si–Sc–Zr alloy with cold-rolling and aging processes was studied. The result shows that the addition of Sc and Zr elements significantly refines the grains of the Al–Mg–Si alloy during casting. The cold rolling promotes the Al–Sc(Zr) precipitation. The precipitate strengthening increases with increasing roll reduction. The EC of the cold rolling?+?aging Al–Mg–Si–Sc–Zr alloy increases with increasing rolling reductions. The combination effects of the precipitation hardening and DRX softening during the aging process lead to the similar peak hardness values of around 70?HV of the rolled Al–Mg–Si–Sc–Zr alloy with the different reductions.     

Precipitation sequence in a SiC/Al-Mg2Si alloy composite material

The precipitation sequence of an Al-1.0mass%Mg₂Si composite material having 8 vol.% SiC particles was investigated by Vickers micro hardness and specific electrical resistivity measurements, and by TEM observation. The formation of GP zones was suppressed in the composite material and its age-hardenability was reduced. Distribution of precipitates in the composite material was coarser and their size was larger than that in the Al-1.0mass%Mg₂Si alloy (base alloy). Some types of precipitates in the composite material were not similar to those found in the base alloy but were similar to those in an Al-1.0mass%Mg₂Si alloys with excess silicon (the excess Si alloy). Especially, the metastable phases in the composite material aged at 473 K belonged to the type-A, type-B and type-C precipitates, which are typical metastable phases in the excess Si alloy, instead of the phase that is a typical metastable phase in quasi-binary Al-Mg₂Si alloys. The dislocations had little effect on the aging process of this composite material, because of the small number of dislocations introduced by the quenching after solution treatment.     

Effect of thermomechanical treatment on spray formed Cu – Ni – Si alloy

Abstract

The heat treatment response of a spray formed Cu – 2.4Ni – 0.6Si (wt-%) alloy has been investigated. The spray formed alloy was given various thermomechanical treatments prior to isothermal aging. These treatments included solutionising and/or cold rolling with different reductions in original thickness. The variation in hardness and electrical conductivity of the alloys was measured as a function of the aging time. The results indicated the highest peak hardness value of ~250 kg mm^-2 for the alloy aged after solution treatment and cold rolling to 40% reduction in thickness, compared with the maximum hardness of 220 kg mm^-2 for specimens aged directly in the as spray formed condition. However, the electrical conductivity after aging was observed to be a maximum of 65%IACS (International Annealed Copper Standard) in specimens cold rolled to 80% reduction in thickness before aging. The aging response was observed to accelerate with the degree of cold working. Optical, scanning electron and transmission electron microscopy were used for microstructural characterisation of the materials. Precipitation of the second phase was observed to dominate in deformation bands. The alloy showed evidence of discontinuous precipitation, particularly when the alloys were cold rolled before aging. The onset of discontinuous precipitation led to a drastic deterioration in hardness of the alloys. The precipitation behaviour of the alloy is discussed in the light of microstructural characteristics associated with various processing conditions of the alloy.     

On the role of matrix grain size and particulate reinforcement on the hardness of powder metallurgy Al–Mg–Si/MoSi2 composites

Six Al–Mg–Si composites reinforced with 15 vol.% of MoSi₂ intermetallic particles, together with three unreinforced monolith Al–Mg–Si (AA6061) alloys have been processed by powder metallurgy to quantify the roles of alloy matrix grain size and reinforcement particle on their solutionized hardness and ageing response. In the range studied, hardness of solutionized composites follows a Hall–Petch mechanism. Moreover, it can be rationalised as the sum of the hardness of the alloy matrix with the same matrix grain size (d) and a term H_R, that accounts for 17–27% of total hardness, is roughly constant and independent of reinforcing size and distribution. Matrix grain size is responsible for 50–65% of hardness, whereas the contributions of solid solution and Orowan strengthenings account for 17–26%. Upon heat treatment at 170 °C, hardening ability decreases linearly with d^?1/2, fitting all data points to a single equation independently of whether they correspond to the composites or to the monolith alloys.     

微量Mg元素添加对Cu-Cr合金析出行为及性能的影响

通过熔炼铸造工艺制备了Cu-Cr和Cu-Cr-Mg合金,评价了Mg元素对Cu-Cr合金硬度、导电和抗软化性能的影响,研究了Mg元素对Cu-Cr合金析出相的细化作用,探讨了Mg元素的迁移行为。结果表明,相比于Cu-Cr二元合金,时效态Cu-Cr-Mg合金具有更高的硬度和软化温度,且保持较高的导电性能。两种合金的主要时效强化相均为纳米Cr析出相,Mg元素的加入抑制了纳米沉淀相的长大和结构转变,峰时效态Cu-Cr-Mg合金的析出相与基体可能仍保持共格界面关系,过时效态合金中出现与Heulser相结构相同的析出相,且峰时效态Cu-Cr-Mg合金经过高温保温处理后,其强化相的尺寸明显小于Cu-Cr合金析出相。EDS的结果表明,在时效初期Mg和Cr共存于析出相内部,而在时效后期析出相内部只有Cr元素存在,Mg元素发生迁移,同时理论估算结果显示,Mg元素可明显降低Cu(fcc)/Cr(bcc)之间的界面能,导致其偏聚于基体/析出相界面处,这可能是Mg元素能够细化析出相和提高合金性能的主要原因。     

Microstructural change and precipitation hardening in melt-spun Mg–X–Ca alloys

Mg–Al–Si–Ca and Mg–Zn–Ca base alloys were rapidly solidified by melt spinning at the cooling rate of about a million K/s. The melt-spun ribbons were aged in the range 100–400°C for 1 h. The effect of additional elements on microstructural change and precipitation hardening after heat treatment was investigated using TEM, XRD and a Vickers microhardness tester. Age hardening occurred after aging at 200°C in the Mg–Al–Si–Ca alloys mainly due to the formation of Al₂Ca and Mg₂Ca phases, whereas in the Mg–Zn–Ca alloys mostly due to the distribution of Mg₂Ca. TEM results revealed that spherical Al₂Ca precipitate has the coherent interface with the matrix. Considering the total amount of additional elements, Mg–Zn–Ca alloys showed higher hardness and smaller size of precipitates than Mg–Al–Si–Ca alloys. With the increase of Ca content, the hardness values of the aged ribbons were increased. Among the alloys, Mg–6Zn–5Ca alloy showed the maximum value of age hardening peak(H_v:180) after aging at 200°C for 1 h.     

High damping properties of Mg–Si binary hypoeutectic alloys

The damping properties of as-cast Mg–Si hypoeutectic alloys with Si contents of 0.25, 0.5, 1 wt.% were investigated by Dynamic Mechanical Analysis (DMA), respectively. The results show that the Si content has an interesting influence on the damping properties due to the primary cyrstallized Mg₂Si. The damping capacities of high damping Mg–Si hypoeutectic alloys are strain amplitude strongly dependent while the strain amplitude weakly dependent part hardly appears due to very few Si dissolved in matrix. In addition, the damping measurement of Mg–0.5 wt.% Si alloy with increasing temperature was carried out and the grain boundary peak is detected.     

A study on the mechanical properties of cryorolled Al–Mg–Si alloy

The mechanical properties of a precipitation hardenable Al–Mg–Si alloy subjected to cryorolling and ageing treatments are reported in this present work. The severe strain induced during cryorolling of Al–Mg–Si alloys in the solid solutionised state produces ultrafine microstructures with improved mechanical properties such as strength and hardness. The improved strength and hardness of cryorolled alloys are due to the grain size effect and higher dislocation density. The ageing treatment of cryorolled Al–Mg–Si alloys has improved its strength and ductility significantly due to the precipitation hardening and grain coarsening mechanisms, respectively. The reduction in dimple size of cryorolled Al–Mg–Si alloy upon failure confirms the grain refinement and strain hardening mechanism operating in the severely deformed samples.     

Effect of Sn on the Microstructure and Mechanical Properties of Mg-5Al-2Si Alloys

The effect of Sn addition on the microstructures and mechanical properties of Mg-5Al-2Si alloys was investigated with variations of Sn contents （3 and 6 wt pct）. The microstructure of the alloy was characterized by the presence of Mg2Sn particles within matrix and at grain boundaries. As the Sn contents increased, yield and ultimate tensile strength were increased at room temperatures and 150℃. Creep properties were improved with the increasing amount of Sn due to the fine precipitation of Mg2Sn phases within grain during creep.     

Microstructure characterization and tensile properties of squeeze-cast AlSiMg alloys

A research program was conducted to study the effects of squeeze pressure (70, 100 and 160 MPa) and heat treatment T6 on the structure, hardness and tensile properties of cast Al6Si0.3Mg alloys. The influence of squeeze pressure on macro- and microstructures of Al6Si0.3Mg alloys has been investigated. Some of castings were solution treated at 540 °C for various times and others were subjected to aging at 170 °C after solution treatment. The results indicated that precipitation occurred within about 30 min for both cast and squeeze cast alloys. The hardness began to increase and maximum values were observed after about 10 h for as-cast alloy. Increasing of squeeze pressure (70–160 MPa) accelerated strength of the alloys from 8 to 4 h, respectively. Squeeze pressures decreased the percentage of porosity and increased the density, also it decreased the grain size of α-Al and modified the Si eutectic. Hardness and tensile properties increased with both heat treatment and increasing of squeeze pressure.     

Microstructure and properties of Cu–Mg alloy treated by internal oxidation

A Cu–0.24Mg alloy bar was treated by internal oxidation using Cu₂O as an oxidiser at 1123–1273?K for 10?h. The thermodynamic diagram for oxidation of a Cu–Mg alloy was confirmed by the critical oxygen pressure. The results show that the thickness of the MgO/Cu layer and the electrical conductivity of the Cu–0.24Mg alloy increase with increasing internal oxidation temperature, whereas the average hardness of the MgO/Cu layer initially increases and subsequently decreases. Examination of the microstructure of the MgO/Cu layer revealed that Mg precipitation in the form of MgO particles and their uniform dispersion in the Cu matrix were the primary reasons for increases in the comprehensive properties of the Cu–Mg alloy treated by internal oxidation.     

Enhanced mechanical properties and electrical conductivity in ultrafine-grained Al alloy processed via ECAP-PC

The objective of this work is to study the effect of grain refinement using equal channel angular pressing with parallel channels (ECAP-PC) on microstructure, mechanical properties, and electrical conductivity of an Al–Mg–Si alloy. The coarse grained (CG) material is subjected to ECAP-PC processing at 100 °C for 1, 2, and 6 passes. Mechanical behavior of the Al–Mg–Si alloy after ECAP-PC processing and its electrical conductivity are analyzed with respect to the microstructure developed during ECAP-PC processing. The effect of artificial aging (AA) on the microstructure, mechanical properties, and electrical conductivity of the ECAP-PC processed Al–Mg–Si alloy is investigated. It is shown that the microstructure developed during ECAP-PC processing affects the kinetics of the aging process that, in turn, affects the mechanical properties and electrical conductivity of the material. It is demonstrated that both mechanical properties and electrical conductivity of the Al–Mg–Si alloy can be simultaneously enhanced via intelligent microstructural design through optimization of the thermo-mechanical processing applied to this material.     

Effects of Cu content on microstructure and mechanical properties of Al–14.5Si–0.5Mg alloy

This study elucidates how Cu content affects the microstructure and mechanical properties of Al–14.5Si–0.5Mg alloy, by adding 4.65 wt.% and 0.52 wt.% Cu. Different Fe-bearing phases were found in the two alloys. The acicular β-Al₅FeSi was found only in the high-Cu alloy. In the low-Cu alloy, Al₈Mg₃FeSi₆ was the Fe-bearing phase. Tensile testing indicated that the low-Cu alloy containing Al₈Mg₃FeSi₆ had higher UTS and elongation than the high-Cu alloy containing the acicular β-Al₅FeSi. It is believed that the presence of the acicular β-Al₅FeSi in the high-Cu alloy increased the number of crack initiators and brittleness of the alloy. Increasing Cu content in the Al–14.5Si–0.5Mg alloy also promoted solution hardening and precipitation hardening under as-quenched and aging conditions, respectively. The hardness of the high-Cu alloy therefore exceeded that of low-Cu alloy.     

时效处理对Al-Zr-Sc(-Er)合金组织和性能的影响EI北大核心CSCD

通过透射电镜(TEM)和扫描透射电镜(STEM)以及硬度、电导率测试等方法系统研究了时效处理对Al-Zr-Sc三元合金以及Al-Zr-Sc-Er四元合金显微组织和性能的影响。结果表明:对于Al-Zr-Sc合金,增加Sc含量,可显著提高合金时效响应速率、峰值硬度和热稳定性;增加Zr含量,显著提高了合金硬度和热稳定性,但会降低电导率。在Al-Zr-Sc合金中添加Er,进一步提高了合金的时效响应速率,促进了Zr,Sc的脱溶析出。Er与Zr,Sc形成具有核-双壳结构的Al 3(Er,Sc,Zr)相,明显改善合金的硬度和电导率。经300℃单级时效,实验合金硬度较高,但电导率相对较低;经400℃单级时效,实验合金时效响应速率加快,电导率明显提高,但硬度显著下降;经300℃/24 h+400℃的双级时效实验合金可获得电导率、强度和热稳定性的良好匹配。     

Microstructures,mechanical and cytocompatibility of degradable Mg–Zn based orthopedic biomaterials

The Mg–1Zn–xSr (x = 0.2, 0.5, 0.8 and 1 wt.%) alloys have been prepared by zone purifying solidification followed by backward extrusion (BE). The grain size was reduced and the hardness was improved with the increased concentration of strontium (Sr) after backward extrusion. The BE–Mg–1Zn–0.8Sr alloy was mostly composed of fine precipitates (MgZn and Mg₁₇Sr₂) and Mg matrix. At the same time, the mechanical properties of BE–Mg–Zn–Sr alloys were increased with the increment of strontium, which were strongly associated with fine average grain size and homogeneous secondary precipitates. The degradation rate is significantly increased when Sr content is over 0.8 wt.%. The homogenous degradation rate is achieved. The degradation products show good biocompatibility evaluated by MTT method using L929 cell line. It is demonstrated that the micro-alloying element of Sr is a potential approach to develop novel Mg–Zn based biomaterials.     

Microstructural change and precipitation hardening in melt–spun Mg–X–Ca alloys

Mg–Al–Si–Ca and Mg–Zn–Ca base alloys were rapidly solidified bymelt spinning at the cooling rate of about a million K/s. The melt-spun ribbons were aged in the range 100–400%C for 1 h. The effect of additional elements on microstructural change and precipitation hardening after heat treatment was investigated using TEM, XRD and a Vickers microhardness tester. Age hardening occurred after aging at 200%C in the Mg–Al–Si–Caalloys mainly due to the formation of Al₂Ca and Mg₂Ca phases, whereas in the Mg–Zn–Ca alloys mostly due to the distribution of Mg₂Ca. TEM results revealed that spherical Al₂Ca precipitate has the coherent interface with the matrix. Considering the total amount of additional elements, Mg–Zn–Ca alloys showed higher hardness and smaller size of precipitates than Mg–Al–Si–Ca alloys. With the increase of Ca content, the hardness values of the aged ribbons were increased. Among the alloys, Mg–6Zn–5Ca alloy showed the maximum value of age hardening peak(H_v:180) after aging at 200%C for 1h.     

Effect of annealing on precipitation, microstructural stability, and mechanical properties of cryorolled Al 6063 alloy

The effect of annealing on precipitation, microstructural stability, and mechanical properties of cryorolled Al 6063 alloy has been investigated in the present work employing hardness measurements, tensile test, XRD, DSC, EBSD, and TEM. The solution-treated bulk Al 6063 alloy was subjected to cryorolling to produce ultrafine grain structures and subsequently annealing treatment to investigate its thermal stability. The CR Al 6063 alloys with ultrafine-grained microstructure are thermally stable up to 250 °C as observed in the present work. Within the range of 150–225 °C, the size of small precipitate particles is <1 μm. These small precipitate particles pin the grain boundaries due to Zener drag effect, due to which the grain growth is retarded. The hardness and tensile strength of the cryorolled Al 6063 alloys have decreased upon subjecting it to annealing treatment (150–250 °C).