Peak Hardness Values Research Articles

Quality Enhancement of TIG Welded Al6061 SiCp Composites by Age Hardening Process

Aluminium and its alloys have exceptional corrosion resistant properties, simplicity of fabrication and extraordinary specific strength-to-weight ratio. The main objective of this study is to explore the effect of age hardening on the mechanical properties of tungsten inert gas (TIG) welded joints of the composite. This study highlights the enrichment in mechanical properties like hardness and tensile strength of TIG welded Al6061-SiC composites. A single-pass TIG welding using 5356 filler material is carried out on the composite with varying percentages of SiC having 25 µm. The hardness and tensile strength of the weld zone in as-weld condition is measured. The samples are then subjected to age hardening treatment at different temperatures and the peak hardness values are determined. The tensile strength is noted, and these values are compared with the values of the as-weld condition. The microstructure of the fracture surface in as-weld and peak aged condition is taken and the type of failure mode is found out. X-ray diffraction (XRD) spectra of the peak-aged sample is also considered for the analysis. The results indicated that there was significant influence leading to substantial improvement of hardness and tensile strength values of the samples after the age hardening process.

Heat Treatment Optimization in Al-Cu-Mg-Si Alloys, with or without Prior Deformation

The properties of Al-Cu-Mg alloys simultaneously depend on dissolving the maximum amount of Cu and Mg in the solution treatment and on achieving optimal ageing. The aim of this study is to analyze the effect on an Al-Cu4.5-Mg1.5-Si0.75 alloy, manufactured by continuous casting and hot rolling until achieving a reduction in its cross-section greater than 90%, of the dwell time at the solution temperature, 495 °C (4, 8, and 24 h), of the different ageing temperatures (160, 180, and 200 °C), and of cold rolling prior to ageing. The microstructural variations underwent the material during its manufacturing process, form its continuous casting to subsequent hot rolling, were analyzed by means of optical microscopy (OM) and scanning electronic microscopy (SEM), with characteristic energy dispersive X-ray (EDX) microanalysis. The crystalline phases present after the different solution and natural ageing treatments were identified and quantified by means of X-ray diffraction (XRD), concluding that Mg is easier to dissolve than Cu. The transient states associated with the Mg2Si phase are the most abundant. However, the longer the dwell time at the solution temperature, the greater the weight percentage of the transient states associated with the Al2Cu phase during ageing. The higher the ageing temperature, the faster the peak hardness is reached, but the lower its value. The ageing temperature that allows the highest hardness to be obtained was 160 °C. The maximum hardness value reached was 162 HV, obtained after a solution treatment at 495 °C for 4 h and ageing at 160 °C for 50 h. By means of prior cold rolling, the peak hardness values are reached more quickly and their values slightly exceed those obtained without this deformation. With ageing at 180 °C, 168 HV are reached after 6 h at this temperature.

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

ABSTRACTThe 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.

Microstructural Characterization of Surface Softening Behavior for Cu-Bearing Martensitic Steels after Laser Surface Heat Treatment

The surface hardening and softening behavior of two types of medium carbon martensitic steel (AISI P20-improved and AISI P21) after laser-assisted heat treatment was quantitatively compared. The laser-assisted heat treatment was performed using a high-power diode laser with in situ temperature and laser power control (two-color pyrometer system). For AISI P20-improved steel, the peak hardness value within the hardening zone was approximately 640 HV after laser-assisted heat treatment at a temperature of 1473 K. In other words, the hardness increased by 120% from the base metal level (290 HV). However, for AISI P21 steel, the hardness within the heat-treated zone did not change from that of the base metal (410 HV), despite being accompanied by martensite transformation. Moreover, it was clearly observed that the hardness dropped below the level of the base metal at the boundary between the heat-treated zone and the base metal region, forming a softening zone. This softening behavior was strongly related to coarsening and a looser distribution of Cu precipitates compared with that of the base metal region, despite the same matrix phase (i.e., tempered martensite) existing in the softening zone and in the base metal region.

Microstructure and mechanical properties of strontium-modified ADC12 alloy processed by heat treatment

The effects of heat treatment and strontium (Sr) addition on the microstructure and mechanical properties of ADC12 alloys were investigated, and two-stage solution treatment was introduced. The results indicated that the addition of Sr obviously refined the microstructure of ADC12 alloys. When 0.05 wt% Sr was added into the alloy, the eutectic Si phase was fully modified into fine fibrous structure; α-Al and β-Al5FeSi phases were best refined; and the eutectic Al2Cu phase was modified into block-like Al2Cu phase that continuously distributed at the grain boundary. The ultimate tensile strength (UTS) (270.63 MPa) and elongation (3.19%) were increased by 51.2% and 73.4% respectively compared with unmodified alloys. After the two-stage solution treatment (500 °C, 6 h+520 °C, 4 h), for 0.05 wt% Sr modified ADC12 alloys, the Si phases transformed into fine particle structure and Al2Cu phases were fully dissolved. The peak hardness value of the alloys processed by the two-stage solution treatment was increased by 8.3% and 6.8% respectively compared to solution treatment at 500 °C and 520 °C. After the aging treatment (175 °C, 7 h), the hardness and UTS were increased by 38.73% and 13.96% respectively when compared with the unmodified alloy.

He ion implantation induced He bubbles and hardness in tungsten

The pure tungsten was implanted with 500 keV helium (He) ions to a fluence of 1.0 × 1017 ions/cm2 at RT and 800 °C. After the implantation, cross-sectional transmission electron microscope (TEM) and nano-indentation measurements were used to investigate the He bubbles and hardness profiles induced by He implantation. Visible He bubbles were observed only in the damage peak region at RT but in the whole damage region at 800 °C. The size of He bubbles at 800 °C increased with increasing depths. With increasing the implantation temperature from RT to 800 °C, the size of He bubbles in the damage peak regions increased. The nano-indentation tests indicated that hardening was induced by He implantation at RT and 800 °C. The implantation induced peak hardness values were the same at both temperatures, but the hardness peaks moved to the surface with increasing temperatures. The formation of He bubbles and the contributions of their distribution and sizes to the hardness were discussed.

Microstructural and Mechanical Characterization of Al-0.80Mg-0.85Si-0.3Zr Alloy

Abstract In this study, Al-0.80Mg-0.85Si alloy was modified with the addition of 0.3 wt.-% zirconium and the variation of microstructural features and mechanical properties were investigated. In order to produce the billets, vertical direct chill casting method was used and billets were homogenized at 580 °C for 6 h. Homogenized billets were subjected to aging practice following three stages: (i) solution annealing at 550 °C for 3 h, (ii) quenching in water, (iii) aging at 180 °C between 0 and 20 h. The hardness measurements were performed for the alloys following the aging process. It was observed that peak hardness value of Al-0.80Mg-0.85Si alloy increased with the addition of zirconium. This finding was very useful to obtain aging parameters for the extruded hollow profiles which are commonly used in automotive industry. Standard tensile tests were applied to aged profiles at room temperature and the results showed that modified alloy had higher mechanical properties compared to the non-modified alloy.

Effect of Homogenizing and Age Hardening on Mechanical Property Enhancement of TIG Welded Al6061 SiC<sub>p</sub> Composites

This paper explains the type of heat treatments used to improve the bulk hardness and tensile properties of Tungsten Inert Gas (TIG) welded Al6061-SiC reinforced composites. Composites with 8, 10 and 12 wt% of SiC (25 μm) are TIG welded using ER5356 filler material and the hardness, tensile property and microstructural analysis in as weld condition is carried out. Age hardening heat treatment is performed and peak hardness values are noted at different aging temperatures and subjected to characterization. Al6061-12 wt% SiC shows reduction in tensile strength in comparison with the other two in spite of improvement in hardness. Since hardness is more, there arise ambiguity in knowing the actual cause of decrease in the tensile strength. Optical micrographs of the samples are taken and identified the presence of dendritic segregation as the actual cause for the (UTS) reduction. To remove dendritic segregation, all the as weld samples are subjected to 5h homogenizing at 500°C, age hardened and characterized. The result showed substantial hike in UTS with substantial improvement in hardness, homogeneous distribution of hardness over the cross-section in the weld bead. The depth and distribution of hardness and bulk property improvement are observed by the combined effect of homogenizing and low temperature age hardening.

Cryo-conditioned rocky coast systems: A case study from Wilczekodden, Svalbard

This paper presents the results of an investigation into the processes controlling development of a cryo-conditioned rock coast system in Hornsund, Svalbard. A suite of nested geomorphological and geophysical methods have been applied to characterise the functioning of rock cliffs and shore platforms influenced by lithological control and geomorphic processes driven by polar coast environments. Electrical resistivity tomography (ERT) surveys have been used to investigate permafrost control on rock coast dynamics and reveal the strong interaction with marine processes in High Arctic coastal settings. Schmidt hammer rock tests, demonstrated strong spatial control on the degree of rock weathering (rock strength) along High Arctic rock coasts. Elevation controlled geomorphic zones are identified and linked to distinct processes and mechanisms, transitioning from peak hardness values at the ice foot through the wave and storm dominated scour zones to the lowest values on the cliff tops, where the effects of periglacial weathering dominate. Observations of rock surface change using a traversing micro-erosion meter (TMEM) indicate that significant changes in erosion rates occur at the junction between the shore platform and the cliff toe, where rock erosion is facilitated by frequent wetting and drying and operation of nivation and sea ice processes (formation and melting of snow patches and icefoot complexes). The results are synthesised to propose a new conceptual model of High Arctic rock coast systems, with the aim of contributing towards a unifying concept of cold region landscape evolution and providing direction for future research regarding the state of polar rock coasts.

Effect of Trace Element Hf on the Precipitation Process and Recrystallization Resistance of Al-Er-Zr Alloys

Vickers hardness and electric conductivity measurements as well as micro-structure analysis were used to investigate the effects of trace element Hf atoms on the precipitation and recrystallization resistance in Al-Er-Zr alloys. The results of the present study indicated that the behaviors of precipitation process in Al-0.04Er-0.08Zr and Al-0.04Er-0.08Zr-0.05Hf (at. %) alloys are similar. When alloys were annealed at 350 °C for 96h, the nanoscale and coherent Al3(Er, Zr) and Al3(Er, Zr, Hf) precipitates form, corresponding to the peak hardness values of 56.2 ± 0.9 (ternary alloy), 58.9 ± 1.5 HV (quaternary alloy), respectively. The higher peak hardness in Al-0.04Er-0.08Zr-0.05Hf alloys mainly benefit from the decomposition of Hf. It was shown that the existence of precipitates could improve the recrystallization resistance obviously. Due to the similar retarding force, recrystallization temperatures of both alloys are almost the same, approximate 450 °C.

Helium irradiation induced hardening in MNHS steels

A recently developed reduced activation martensitic MNHS steel was irradiated with 200keV helium (He) ions to a fluence of 1.0×1020ions/m2 at 300°C and 1.0×1021ions/m2 at 300°C and 450°C. After irradiation, transmission electron microscopy (TEM) and nano-indentation measurements were used to investigate the hardness change and defects induced by He irradiation. Two kinds of defects including He bubbles and dislocation loops are observed by TEM. Irradiation induces hardening of MNHS steels and peak hardness values occur in all irradiated samples. Hardness increments induced by He bubbles and dislocation loops are predicted and fitted with the experimental peak hardness increment, based on the dispersed barrier-hardening (DBH) model and the size and number density of the two defects. A good agreement is got between the predicted and experimental hardness increment and the obstacle strength factor of He bubbles is a little stronger than the obstacle strength of dislocation loops. Other possible contributions to irradiation induced hardening are also discussed.

Influence of Artificial Aging on the Stir Cast Al6061-SiC Metal Matrix Composites under Different Aging Conditions

The present work aims to improve the microstructure and hardness related properties of age hardened Al6061-SiC reinforced composites produced by a two stage stir casting method. Three composites with 2, 4, and 6wt. % (35-40μm) of SiC reinforcement are subjected to microstructural examination and hardness test at different locations to analyse the uniform distribution of the reinforcements in the matrix. As-cast composites are solution-treated at 558°C, followed by an aging treatment conducted at 100, 150, and 200°C, during which peak hardness values are noted. The peak aged samples are subjected to hardness and wear tests. In line with the objectives, ranges from 80-100% and 120-145% additional increase in hardness values are observed over as-cast alloy during the aging treatment conducted at 100, 150 and 200°C, respectively. Lower temperature aging shows substantial improvement in hardness and wear resistance over high temperature aging in each respective group. Also higher weight percentages of reinforced composites show excellent wear resistance, due to the presence of eroded iron particles from the counter surface which is regarded as a beneficial effect during the wear test. The presence of SiC particles provides more sites for the nucleation of fine precipitates. These fine precipitates hinder the movement of dislocation and thus increases hardness as well as wear resistance after the precipitation hardening treatment

Effect of Al Addition on ω Precipitation and Age Hardening of Ti-Al-Mo-Fe Alloys

The effect of Al addition on ω precipitation and age-hardening behavior of Ti-9.2Mo-2Fe and Ti-2Al-9.2Mo-2Fe alloy during aging treatment was investigated. The results showed that athermal and isothermal ω phase formation in Ti-2Al-9.2Mo-2Fe alloy was suppressed to a certain extent due to Al addition. In addition, a small amount of athermal ω phase was observed in the β matrix with a size of about ~5 nm during water quenching from above the β transus temperature for both alloys. Isothermal ω formation was also found during aging at temperatures ranging from 573 K to 773 K (300 °C to 500 °C) in both alloys, although it had a limited time of stability at 773 K (500 °C). The hardening due to isothermal ω precipitation exhibited no over-aging as long as ω phase existed in both alloys, and ω phase played a more important role in hardening than α phase. And the ω phase in 50 to 100 nm size exhibited the best hardening effect in Ti-9.2Mo-2Fe alloy. Similarly, α phase with 100 to 200 nm in length showed better hardening effects in Ti-2Al-9.2Mo-2Fe alloy. Both the alloys showed stronger age hardening at an intermediate temperature of 673 K (400 °C) and in the first aging stage at a higher temperature of 773 K (500 °C) due to the sufficiently fine size (50 nm), while they exhibited weaker age hardening at a lower temperature of 573 K (300 °C) and long period aging at a higher temperature of 773 K (500 °C) due to incomplete ω formation and/or coarsening of α phase. No over or peak aging stage was found at 573 K and 673 K (300 °C and 400 °C) during the aging for 72 hours, while the peak hardness values of both alloys aged at 773 K (500 °C) were obtained in the first stage of aging. The hardness of the alloys was very sensitive to size and volume fraction of ω phase, which depends on aging temperature, time, and composition of the involved alloys.

Effects of Zn additions on the microstructure and hardness of Mg–9Al–6Sn alloy

The effects of Zn additions on the age hardening response and microstructure of Mg–9Al–6Sn (wt.%) alloy have been investigated. It is found that the Zn additions can remarkably increase the alloy hardness in the as-quenched condition. The peak hardness value of the Mg–9Al–6Sn alloy increases from 90±0.87HV to 103±3.83HV, when the Zn addition is 3wt.%, which is the highest among the magnesium casting alloys that are free of rare-earth elements. The enhanced hardness in the Mg–9Al–6Sn–3Zn alloy is attributable to an increased volume fraction of smaller Mg2Sn particles in the solution-treated condition and the formation of [0001]Mg Mg17Al12 rods and Mg21(Zn, Al)17 precipitates in the peak-aged condition.

Microstructure and Mechanical Properties of Solution Treatment and Sr-Modification of Al-12%Si-1.5%Cu Alloy

The purpose of this paper was to investigate the effects of solution treatment time and Sr-modification on the microstructure and property of the Al-Si piston alloy. It was found that as-cast microstructures of unmodified and Sr-modified Al-Si alloys consisted of a coarse acicular plate of eutectic Si, <TEX>$Cu_3NiAl_6$</TEX> and <TEX>$Mg_2Si$</TEX> phases in the <TEX>${\alpha}$</TEX>-Al matrix but different in size and morphology. Both size and inter-particle spacing of Si particles were significantly changed by increasing of the solution treatment time. After a short solution treatment, the coarse acicular plate of the eutectic Si appears to be fragmented. Fully modified microstructure of Sr-modified alloy can reduce the solution treatment time to shorter compared to unmodified alloy. The maximum of a peak hardness value is found in the very short solution treatment of both Al-Si piston alloys. Compared to 10 h solution treatment, the solution treatment of 2-4 h is sufficient to achieve appropriate microstructures and hardness. The short solution treatment is very useful to increase the productivity and to reduce the manufacturing cost of the Al-Si piston alloys.

Characterization Study of Aluminium 6061 Hybrid Composite

Aluminium matrix composites with alumina reinforcements give superior mechanical & physical properties. Their applications in several fields like automobile, aerospace, defense, sports, electronics, bio-medical and other industrial purposes are becoming essential for the last several decades. In the present work, fabrication of hybrid composite was done by Stir casting technique using Al 6061 as a matrix with alumina and silicon carbide (SiC) as reinforcement materials. The weight percentage of alumina is varied from 2 to 4% and the silicon carbide weight percentage is maintained constant at 2%. Hardness and wear tests are performed in the as cast and heat treated conditions. Age hardening treatment was performed on the specimen with solutionizing at 550°C, aging at two temperatures (150 and 200°C) for different time durations. Hardness distribution curves are drawn and peak hardness values are recorded. Hardness increase was very sensitive with respect to the decrease in aging temperature. There was an improvement in wear resistance of the peak aged material when aged at lower temperature. Also increase in weight percent of alumina, increases wear resistance at lower temperature but opposite behavior was seen when aged at higher temperature.

Hardening behavior and phase decomposition in very Ni-rich Nitinol alloys

A series of Ni-rich Nitinol compositions spanning from 53NiTi to 58NiTi (at%) have been solutionized at 1050°C and aged at 400°C, 625 °C, and 750°C for varying times to determine the correlation between microstructure and hardenability. Compositions of 55NiT, 56NiTi, and 57NiTi displayed peak hardness values near 650 VHN upon quenching, which are on par with tool steels. Upon aging at 400°C, all but the 55NiTi and 56NiTi compositions exhibited a decrease in hardness initiating, between 1 and 10h for the lower Ni alloys and after 100h for the highest Ni containing alloys. The high hardness, including the solution treated condition, was attributed to the precipitation of a large volume fraction of nanoscale Ni4Ti3 platelets that resulted in narrow B2 NiTi matrix channels. These channels provided a microstructure-driven strengthening morphology. Upon increasing Ni content to greater than 56NiTi and increasing the aging time and temperature, the Ni4Ti3 phase decomposed to either Ni3Ti2 and/or Ni3Ti with a subsequent loss in hardness. The decomposition morphology between the precipitates was characterized by serial sectioning showing that Ni4Ti3 platelets acted as a heterogeneous nucleation site and subsequent Ni-reservoir during the growth of globular Ni3Ti precipitates.

A study of precipitation strengthening and recrystallization behavior in dilute Al–Er–Hf–Zr alloys

A study on the precipitation hardening and recrystallization behavior of dilute Al–Er–Hf and Al–Er–Hf–Zr alloys has been carried out. The results show that both Al–0.045Er–0.18Hf and Al–0.045Er–0.08Zr–0.1Hf alloys can obtain remarkable age strengthening effect and recrystallization resistance. The precipitation hardening rate of Al–0.045Er–0.08Zr–0.1Hf is accelerated compared with that of the Al–0.045Er–0.18Hf alloy due to substituting 0.08at% Zr for Hf, which can be ascribed to the sequential precipitation of solute elements on the basis of the disparity in their intrinsic diffusivities (DEr>DZr>DHf). The peak hardness values for the Al–0.045Er–0.08Zr–0.1Hf are 644MPa and 662MPa after isochronal aging to 450°C and isothermal aging at 350°C for 84h, respectively, which are higher than those of the Al–0.045Er–0.18Hf alloy. The recrystallization temperature of Al–Er–Hf–Zr alloy is 450°C, about 25°C higher than that of the Al–Er–Hf alloy due to the larger f/r ratio of precipitates in Al–Er–Hf–Zr alloys.

Thermal stability and oxidation resistance of arc evaporated TiAlN, TaAlN, TiAlTaN, and TiAlN/TaAlN coatings

Phase stability and oxidation resistance are main objectives when synthesising hard and protective coatings for applications requiring also high thermal stability. Even though TiAlN is a well-studied and nowadays widely used high performance coating, the demand for further optimisation is omnipresent. Recent investigations on quaternary compounds demonstrate that the alloying of Ta to TiAlN films not only results in enhanced phase stability, but also in a significantly increased oxidation resistance. In this study we address thermal investigations of reactive cathodic arc evaporated coatings and elucidate the diverse performance of monolithically grown TiAlN, TaAlN, TiAlTaN, and a multilayered architecture of TiAlN and TaAlN layers. Subtle variations of the bilayer period between 30 and 38nm were realised by varying the arc current at the TaAl cathode.Our research demonstrates that the quaternary Ti0.45Al0.36Ta0.19N and the multilayered TiAlN/TaAlN coatings feature enhanced mechanical properties and thermal stability as compared with their monolithically grown constituents Ti0.54Al0.46N and Ta0.89Al0.11N. All coatings synthesised exhibit as-deposited hardness values of 32±1GPa, but only the quaternary Ti0.45Al0.36Ta0.19N and the multilayered TiAlN/TaAlN coatings demonstrate pronounced age-hardening with peak hardness values of 37±2 and 35±2GPa for annealing temperatures of ~1000 and 1100°C, respectively. Complementary X-ray diffraction and differential scanning calorimetry confirm their enhanced phase stability. Even though, also the multilayered design shifts the formation of wurtzite-structured AlN to higher temperatures, only quaternary Ti0.45Al0.36Ta0.19N could withstand ambient air oxidation at 850°C for 20h. This is based on the ability of forming a nearly single-phased dense protective mixed oxide scale, having an outermost Al-rich composition. Approximately 70% of this quaternary nitride remained unaffected from oxidation. With the present study we conclusively demonstrate that thermomechanical properties of cathodic arc deposited TiAlN coatings can significantly be enhanced by either forming a quaternary compound or sophisticated architectural design with tantalum, both allow for wide-ranged industrial applications.

The mechanical properties of dissimilar resistance spot-welded DP600–DP1000 steel joints for automotive applications

A study was conducted to investigate the microstructure and the mechanical properties of dissimilar resistance spot welds between steel sheets of DP600 and DP1000 using different welding currents for automotive applications. Microstructural characterization, microhardness tests and tensile shear tests of the joints were conducted. The dissimilar joints had three main microstructural zones: the base metals; the heat-affected zones of both steels; the fusion zone. Additionally, the DP1000 side of the joints also had a transition zone between the heat-affected zone and the base metal, which exhibited significant softening. Such a soft transition zone was not observed on the DP600 side. The peak hardness values were observed in the centre heat-affected zones of both sides of the joints. The welding current significantly influenced the microstructure and the mechanical properties of the joints. With increasing welding current, the nugget size increased almost linearly and the widths of the heat-affected zones on both sides became smaller. The use of higher welding currents reduced the microhardness values in the outer heat-affected zones of both sides and the fusion zone of the joints; the hardness values in these zones decreased almost linearly with increasing welding current. For a welding current of up to 10 kA, the tensile shear loads of the joints increased linearly with increasing welding current. The peak values of the tensile shear load and tensile deformation were obtained for the joints welded with a current of 10 kA. All joints exhibited the full button pull-out failure mode under the tensile shear loading test. The failure location of all joints was in the centre heat-affected zone. The joints welded with relatively lower welding currents (8–9.5 kA) failed on the DP1000 side, while the failure of the other joints fabricated with relatively higher welding currents (10–11 kA) was located on the DP600 side of the weld.