Influence of short-term heat treatment on the microstructure and mechanical properties of EN AW-6060 T4 extrusion profiles—Part B

In the automotive industry aluminium and its corresponding semi-finished products contribute an essential part to the aim of weight reduction in car body structures. Aluminium alloys of the 6000 series with Mg and Si contents are preferred because of the possibility to increase strength by ageing processes. However, the cold formability in comparison to other materials like mild steels is quite low and due to this, complex parts are only producible at higher temperatures. Therefore, the so called Tailor Heat Treatment was developed to improve the cold formability of aluminium alloys. In this approach, a short-term heat treatment is conducted to achieve a local softening of the material due to dissolution of Mg and Si clusters (retrogression). This effect is used to improve the material flow, relief critical forming zones and enhance the overall formability of the material. Afterwards, strength can be increased again by ageing processes. However, up till now a holistic process understanding, taking into account all process parameters as well as a microstructural explanation is missing. Therefore, the focus of the fundamental investigations lies on connections between the mechanical properties and short-term heat treatment with industry-relevant heating rates as well as natural and artificial ageing process. Conclusively, the evolution of the mechanical properties with regard to the natural ageing process is compared with findings of DSC analysis, which were discussed in Part A. Based on these results, a process window is derived for the subsequent forming process and the final mechanical properties of the final part in dependency of the forming history as well as the artificial ageing process, are identified.     

Influence of Hot Deformation on Mechanical Properties and Microstructure of a Twin-Roll Cast Aluminium Alloy EN AW-6082

Thin strips of medium- and high-strength age-hardening aluminium alloys are widely used in the automotive industry. Reducing their production costs caused by high energy consumption is an actual challenge. The implementation of the twin-roll casting technology is promising. However, mechanical properties of directly cast high-alloyed thin aluminium strips are oftentimes inadequate to standard specifications. In this work, the influence of a hot deformation following a twin-roll cast strip process on the mechanical properties and microstructure is investigated. For this study strips of age-hardening aluminium alloy EN AW-6082—manufactured at a laboratory scaled twin-roll caster—were single-pass rolled at temperatures of 420 °C and true strains of up to 0.5. The mechanical properties of the as-cast and by different strains hot deformed material in the soft-annealed and age-hardened states were characterized by tensile tests. The results reveal that the twin-roll cast material features the necessary strength properties, though it does not meet the standard requirements for ductility. Furthermore, the required minimum strain during hot rolling that is necessary to ascertain the standard specifications has been determined. Based on micrographs, the uniformity of the mechanical properties and of the microstructure as a result of recrystallization due to hot metal forming and heat treatment were determined. A fine-grain microstructure and satisfactory material ductility after prior rolling with a true strain above 0.41 for the age-hardened state T6 and above 0.1 for the soft-annealed state O have been established.     

固溶处理和人工时效对Al-Cu合金显微组织和力学性能的影响(英文)

对Al-Cu合金进行析出强化和人工时效处理以获得优异的力学性能,如高的强度、好的韧性。其热处理工艺条件为:510～530℃固溶处理2h;60℃水淬;160～190℃人工时效2～8h。采用光学显微镜、扫描电镜、能谱分析、透射电镜和拉伸实验对经固溶和人工时效处理的Al-Cu合金的组织和力学性能进行表征。固溶处理实验结果表明,Al-Cu合金的力学性能随着固溶处理温度的升高先增加,然后降低。这是由于Al-Cu合金的残余相逐渐溶解进入基体中,从而导致析出相的数量和再结晶晶粒尺寸不断增加。相较于固溶处理温度,固溶处理时间对Al-Cu合金的影响较小。人工时效处理实验结果表明,合金经180℃时效8h,可以获得最大的拉伸强度。合金的最大拉伸强度和屈服强度随着时效时间的延长和温度的升高而升高。     

预变形结合人工时效对Al-Mg-Si合金力学性能的影响

研究预变形结合人工时效处理对AA6060铝合金强度和韧性的影响。对经过均匀化热处理和挤压加工的AA6060铝合金进行固溶处理,然后对材料实施0-10%的预变形并再进行时效处理或者在人工时效过程中进行同步变形。通过对不同时效处理后的合金的显微硬度和拉伸性能分析,发现预变形对材料的时效行为和力学性能有显著影响,它可以使合金的时效速度明显加快。比较预变形和同步变形对人工时效的影响发现,同步变形结合人工时效可以使该合金在更短的时间内得到更好的力学性能。对两种变形对时效行为的影响机理进行了探讨。     

Identification of heat treatments for better formability in an aluminum-lithium alloy sheet

Research in the weight of an automobile is a continuous process among auto manufacturers. The “body in white” (BIW, i.e., the body of the car) deserves attention, being a major contributor to the weight of the vehicle. By virtue of a high strength to weight ratio (density smaller than aluminum) and a higher Young’s modulus than aluminum, aluminum-lithium alloy sheet appears to hold promise as an autobody material. Because auto components are required in large numbers and are formed at room temperature, formability under these conditions becomes significant. Aluminum-lithium alloys acquire, because of aging over a short period of time, a good amount of strength and hence dent resistance. In principle, they can be given, through suitable heat treatments, a high formability as well as dent resistance, i.e., an ideal combination of properties. To this end, tensile properties have been determined for a number of heat treatments comprising three different solutionizing temperatures and for three aging times at each of the three aging temperatures. Considerable influence of heat treatment was observed on the mechanical properties (which in turn characterize both formability and dent resistance), such as the strain hardening exponent, average normal anisotropy, yield stress, ultimate tensile stress, and percentage elongation to failure. For each property, the best three heat treatments leading to a high formability were identified. Consequently, heat treatments that imparted the greatest formability for processes such as deep drawing and stretch forming have been identified. The investigations show that the best heat treatment for one property may not be the best for another property, calling for a compromise to obtain the most practicable heat treatment schedule. Results shed light on not only the biaxial formability but also springback behavior that is important in the BIW components. Further, the properties obtained from the heat treatment giving good formability in deep drawing were used to simulate car body fender and the S-rail using sheet metal forming simulation software PAMSTAMP2G. A comparison of simulation of aluminum-lithium alloy fender and S-rail with those made from steel demonstrates advantages using aluminum-lithium alloys in terms of weight reduction. Finally, based on the current oil prices and the projected demand for oil in the next decade, aluminum-lithium alloys seem to have an edge despite the difficulties in manufacturing, assembly, and joining of the aluminum-lithium components.     

电解低钛汽车轮毂材料的研究

本文应用原位钛合金化、细晶化的电解低钛铝基合金为母材生产汽车轮毂材料——A356合金，对其微观组织及性能进行了研究。研究发现：电解低钛A356合金较传统的熔配加钛A356合金组织细化，一次枝晶细小，二次枝晶臂间距短；经过T5短时处理，硅相球化良好，颗粒细小，强化元素Si、Mg在基体中均匀、弥散析出。电解低钛A356合金具有高强度和高韧性的良好力学性能匹配，σь≥300MPa和δ≥8％的性能比传统熔配加钛的A356合金强度和塑性均可提高20％以上。     

快速冷却对DP1000双相钢激光焊接接头性能的影响

激光焊接DP1000双相先进高强钢的过程中,普遍存在焊接热影响区的软化现象,热影响区的软化严重影响了焊接结构的成形和使用性能. 为了能提高焊接接头的成形和使用性能,采用快速冷却的方式来改善其焊接热影响区的软化问题. 通过拉伸试验、显微硬度测试、扫描电镜和光学显微镜等手段对比研究了1.5 mm厚DP1000双相钢板有无快速冷却的焊接接头中组织和性能的变化. 结果表明,在快速冷却条件下,激光焊接DP1000双相钢的接头热影响区软化区较空冷焊接的窄,软化现象有所改善,强度和塑性均有所提高.     

Mechanical properties of Al–Si–Cu alloys produced by the continuous casting process with heating process

The mechanical properties of aluminium alloys produced by the continuous cast process and heating process (heat-cast-sample) were investigated, where the aluminium alloys are heated continuously to high temperatures for 1 h immediately following heated mould continuous casting (HMC) and sand gravity casting (SGC). The material strength and ductility of the aluminium alloys were irregularly altered depending on the heating temperature. The mechanical properties decreased when the heating temperature increased to 400 °C and were then recovered when the temperature increased to 520 °C. However, these properties decreased again when heated to more than 540 °C. The mechanical properties of the HMC-heat-cast-sample showed overall higher than those for the SGC-sample. In addition to high tensile strength, high ductility was obtained for the HMC-520 °C samples compared with those for the as-cast-sample. Such changes were found to be directly attributable to the different severity of precipitate; moreover the crystal orientation was unchanged even after the heating process.     

Cr对含FeT业纯铜组织和力学性能的影响

研究了Cr的不同加入量（ωcr=0％、0．3％、0．75％和1．2％）对含Fe工业纯铜组织和力学性能的影响。结果表明,Cr与Cu不能形成化合物,可有限固溶于纯铜中,超过部分形成过剩的第二相。固溶时效热处理可析出细小弥散的第二相质点。随Cr含量增大,铸态合金材料的强度、硬度增加。热处理可使铸态力学性能得到进一步提高。少量的Fe对合金的力学性能是有益的。     

热处理对砂型铸造Mg-4Y-2Nd-1Gd-0.4Zr镁合金显微组织和力学性能的影响(英文)

研究热处理工艺对砂型铸造Mg-4Y-2Nd-1Gd-0.4Zr镁合金显微组织和力学性能的影响,分析不同热处理条件下合金的断裂机制,获得最佳热处理工艺。结果表明:Mg–4Y–2Nd–1Gd–0.4Zr合金的最佳T4和T6热处理工艺分别为525°C,8 h和(525°C,8 h)+(225°C,16 h)。在最佳T6热处理条件下,Mg-4Y-2Nd-1Gd-0.4Zr合金的硬度、屈服强度、抗拉强度和伸长率分别为HV91、180 MPa、297 MPa和7.4%。此外,不同状态的Mg-4Y-2Nd-1Gd-0.4Zr镁合金也显示出不同的拉伸断裂方式。     

热处理工艺对微量Mn、Zr作用下的高纯Al-Cu-Mg-Ag合金性能的影响

研究了固溶处理和时效处理对微量Mn、Zr作用下的高纯Al-Cu-Mg-Ag合金性能的影响,结果表明:合金在520～525℃时,可以得到较好的力学性能,固溶时间对性能的影响不大。合金在160℃下时效12h可以达到峰时效,而在180℃下达到峰时效的时间仅需要4h。向Al-Cu-Mg-Ag中添加微量Mn、Zr元素可以大幅度的提高合金的延伸率,但Mn元素的添加却降低合金的抗拉强度,而Zr元素则大幅度的提高了合金的抗拉强度。在合金的耐热性能方面,微量Mn、Zr元素的添加均显著提高Al-Cu-Mg-Ag合金的热稳定性。     

Enhancement of formability of aluminum alloys in multi-stage forming operations by a local intermediate heat treatment

Within this paper a new approach to enhance the formability of aluminum alloys in multi-stage forming processes will be presented. The technology??s key idea is the local adaption of the mechanical properties after a first forming step and their optimization for the subsequent forming operation. The partial change of the mechanical properties is obtained by a short term heat treatment between two forming steps. Based on the new property distribution the material flow during the second forming is improved and the formability of the material can be enhanced. The presented work covers all necessary steps for a successful application of the technology. After a material characterization in dependency of the pre-straining and the heat treatment, the heat affected zone, which is a result of the high heat conductivity of aluminum alloys was analyzed. In the end appropriate heat treatment layouts were designed via numerical simulation and the enhancement of formability was demonstrated with a real multi-stage forming process.     

焊后热处理对异种合金摩擦焊件组织与性能的影响

用金相观察、SEM分析和拉伸试验等方法研究不同的焊后热处理制度对异种合金(Ti2AlNb/TC11)线性摩擦焊接件显微组织与力学性能的影响。结果表明:仅进行时效热处理时,随着保温时间的延长或热处理温度的提高,焊缝两侧热影响区条状α/O相析出量不断增加,焊接接头强度也相应得到提高;固溶及时效热处理后,TC11合金侧热影响区在晶界上析出大量粗条状α相,Ti2AlNb合金侧热影响区晶界主要由条状O相构成,焊接接头强度超出母材TC11合金的强度。     

Optimization of heat treatment of gravity cast Sr-modified B356 aluminum alloy

In recent years, certain foundry processes have made it possible to obtain products with very thin parts, below the 4 mm threshold of the permanent mold casting technology. The safety margins of these castings have been reduced, so the T6 heat treatment conditions adopted for the Al–7Si–Mg alloys need to be investigated to identify the best combination of strength and ductility. Furthermore, the cost and the production time associated with T6 heat treatment have to be optimized. In the present work, an experimental study was carried out to optimize the solution treatment and artificial aging conditions in gravity cast thin bars of B356 aluminum alloy modified with Sr. Two solution temperatures were selected, 530 °C and 550 °C, respectively, with solution time ranging from 2 to 8 h, followed by water quenching and artificial aging at 165 °C with aging time from 2 to 32 h. The results of hardness and tensile tests were correlated with differential scanning calorimetry (DSC) analysis. The best combination of mechanical properties and heat treatment duration was obtained with 2 h solutionizing at 550 °C and 8 h aging at 165 °C. DSC analysis showed that the alloy's mechanical properties reach the maximum value when the β″ phase is completely developed during the artificial aging.     

La-Ce混合稀土对Mg-Al-Mn合金力学性能及耐蚀性能的影响

研究了La-Ce混合稀土对Mg-Al-Mn合金组织形貌、力学性能及耐蚀性的影响。采用T-1200CB坩埚炉冶炼稀土含量(质量分数)分别为4.63%、5.81%、6.18%的Mg-Al-Mn合金。在箱式电阻炉中对研究试样进行430 ℃保温24 h的固溶处理,然后进行200 ℃保温24 h时效处理。对不同热处理状态的试样进行组织观察,对固溶时效后的试样进行拉伸、硬度及盐雾腐蚀试验,从而分析La-Ce混合稀土对Mg-Al-Mn合金显微组织、力学性能及耐蚀性的影响。研究表明,随着合金中的La-Ce混合稀土含量的增加,Mg₁₇Al₁₂相逐渐被Al₄(La, Ce)相代替;硬度、抗拉强度和伸长率都逐渐减小,力学性能下降;合金的腐蚀速率逐渐下降,耐蚀性提高。     

Effects of different tempers on precipitation hardening of 6000 series aluminium alloys

By means of Vickers hardness,mechanical property and formability tests,the effects of different tempers on precipitation hardening of 6000 series aluminium alloys for automotive body sheets were investigated.The results indicate that the short-time pre-aging at 170℃makes for subsequent artificial aging precipitation hardening.With the increase of pre-aging time,the artificial aging hardenability increases.The aging hardening rate reaches the maximum when pre-aging time is up to 10 min,and then it decreases.The short-time pre-aging at 170℃benefits sheets to obtain lower strength under delivery condition and consequently to improve stamping formability of automotive body sheets.The effects of different tempers on precipitation hardening are much more obvious than those of the alloying elements.It is a good treatment schedule to perform pre-aging for 5 min at 170℃right after solution treatment.     

Properties and structure of friction stir welded joints in 1424 and V-1461 (Al–Li) alloys*

The effect of the friction stir welding (FSW) conditions on the structure of welded joint and mechanical properties of 1424 and V-1461 alloys is investigated. FSW is accompanied by the formation of a recrystallized fine-grain microstructure in the welded joint. It is shown that the increase of the heat input to the welded sheets does not increase the average grain size in the weld zone (the average grain size is 1.5–2.2 μm). The tensile strength of the welded joints depends on the welding conditions for both alloys. Special features of the microstructure formed in the zone of the welded joint are discussed and the effect of the microstructure on the mechanical properties of the welded joints and evolution under the effect of heat treatment after FSW are determined.     

添加Ca和Sr元素对ZK61镁合金组织与性能的影响

利用光学显微镜、X射线衍射仪、扫描电镜、Vickers硬度计及拉伸试验机等观察并研究了添加Ca和Sr元素及热处理工艺对ZK61镁合金组织和力学性能的影响。结果表明:单独添加Ca元素时,在ZK61-xCa合金α-Mg基体上析出了形状不规则的MgZn和MgZn2相;复合添加Ca、Sr元素时,在α-Mg基体上形成了沿晶界分布的Mg17Sr2新相。当固溶温度和时间为350℃×12 h,时效温度和时间为200℃×12 h时,合金的组织与性能达到最优。当元素Ca=1.0%,Sr=0.5%时,热处理后合金的性能最优,其抗拉强度为141.9 MPa,伸长率为15.6%,维氏硬度为51.6 HV。     

Effects of Cu content on microstructure and mechanical properties of rheo-diecasting Al-6Zn-2Mg-xCu alloys

A systematic study on how Cu content affects the microstructure and mechanical properties of rheo-diecasting Al-6Zn-2Mg-xCu alloys during solution treatment and ageing heat treatment was conducted. The swirled enthalpy equilibrium device (SEED) was adopted to prepare the semi-solid slurry of Al-6Zn-2Mg-xCu alloys. The microstructure development and mechanical properties were studied using optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), as well as hardness and tensile testing. The grain boundary and shape factor were calculated using image processing software (Image-Pro Plus 6.0). Results show that the alloys are composed of typical globular primary α-Al grains, eutectic phases, and smaller secondary α-Al grains. After solution and ageing heat treatment, the eutectic phases are dissolved into Al matrix when the Cu content is lower than 1.5wt.%, while some eutectic phases transform into Al₂CuMg (S) phases and remain at grain boundaries when Cu content reaches 2wt.%. T6 heat treatment significantly enhances the mechanical properties of rheo-diecasting Al-6Zn-2Mg-xCu alloys. When Cu concentration is 0.5wt.%–1.5wt.%, the ultimate tensile strength, yield strength and elongation of T6 treated alloys rise to around 500 MPa, 420 MPa, and 18%, respectively.

     

初始组织对热挤压Mg-6Al-2Ca-2Sm合金显微组织和力学性能的影响

对铸态Mg-6Al-2Ca-2Sm合金分别进行经固溶和固溶+时效处理获得不同初始组织试样,然后对不同初始组织的试样进行热挤压,研究了不同初始组织对热挤压Mg-6Al-2Ca-2Sm合金显微组织和力学性能的影响。结果表明：铸态合金经热挤压后发生明显的部分再结晶,显微组织得到显著细化;经固溶或固溶+时效处理能够改善合金组织,热挤压后合金显微组织分布更加均匀。初始组织分布能够改善热挤压Mg-6Al-2Ca-2Sm合金室温和高温力学性能,固溶+时效后进行热挤压,Mg-6Al-2Ca-2Sm合金具有最高的抗拉强度和延伸率。