T6 Heat Research Articles

Effect of Zinc and Severe Plastic Deformation on Mechanical Properties of AZ61 Magnesium Alloy.

This study investigates the effects of zinc (4 wt.%) and severe plastic deformation on the mechanical properties of AZ61 magnesium alloy through the stir-casting process. Severe plastic deformation (Equal Channel Angular Pressing (ECAP)) has been performed followed by T4 heat treatment. The microstructural examinations revealed that the addition of 4 wt.% Zn enhances the uniform distribution of β-phase, contributing to a more uniformly corroded surface in corrosive environments. Additionally, dynamic recrystallization (DRX) significantly reduces the grain size of as-cast alloys after undergoing ECAP. The attained mechanical properties demonstrate that after a single ECAP pass, AZ61 + 4 wt.% Zn alloy exhibits the highest yield strength (YS), ultimate compression strength (UCS), and hardness. This research highlights the promising potential of AZ61 + 4 wt.% Zn alloy for enhanced mechanical and corrosion-resistant properties, offering valuable insights for applications in diverse engineering fields.

Extending the mechanical property regime of laser powder bed fusion Sc- and Zr-modified Al6061 alloy by manipulating process parameters and heat treatment

Highly dense compositionally modified Al6061 alloys with Sc and Zr (Al6061MOD) were fabricated using the laser powder bed fusion. The as-built AL6061MOD alloy exhibits a bimodal grain size distribution consisting of coarse columnar grains and ultrafine grains, which is tunable by either varying the printing parameters or post-heat treatment. A high laser energy density along with a lower cooling rate, leaving more time for nucleating primary Al3Sc particles, triggers a higher area fraction of ultrafine grains. The heat treatment-induced evolution of microstructure and mechanical properties is jointly influenced by the size of grains and (Al,Si)3(Sc,Zr) particles. The conventional T6 heat treatment triggers coarsening of grains (∼5.3 μm) and (Al,Si)3(Sc,Zr) particles (∼42 nm), lowering the yield strength (∼280 MPa) compared with that of as-built counterparts. On the contrary, direct aging enhances the yield strength (∼383 MPa) due to the precipitation of nano-sized secondary Al3(Sc,Zr) particles (∼5 nm) as well as retaining the grain size (∼690 nm) of ultrafine grains. Concurrent with the tunable strength, the plasticity behaviors (Lüders band and Portevin-Le Chatelier effect) are manipulated correspondingly with varying microstructure. The broad tailoring of microstructure and mechanical property regime can shed light on designing Al alloys targeting the desired applications by manipulating the printing parameters and heat treatment.

Effect of Short Heat Treatments on the Microstructural Evolution and Hardness of Thixoformed Graphene Reinforced Aluminium Composites

Aluminium metal matrix composites are increasingly being used in numerous industries due to their lightweight nature and high strength. The incorporation of graphene into aluminium metal matrix composites has garnered significant interest owing to graphene's capacity to enhance numerous properties concurrently. Hence, this study aimed to fabricate a 0.3 wt.% graphene nanoplatelets reinforced A356 alloy (GNP-A356) composite through stir casting followed by thixoforming and short T6 heat treatment processes. It also evaluated the microstructure and mechanical properties of GNP-A356 after the thixoforming process and short T6 heat treatment. The microstructure of alloy and composite was confirmed by optical microstructure, field emission scanning electron microscopy images, and X-ray diffraction. Microstructure investigations demonstrate the impact of the stirring process on the structural transformation of the 𝛼-Al phase from the dendritic into a rosette-like and globular-like structure. The result also indicated that there was a transformation of eutectic silicon from the shape of a needle-like to spheroid structure after a short heat treatment, showing the efficiency of T6 heat treatment with a shorter time of solution treatment and ageing. Moreover, the increase in relative density and addition of reinforcement led to a significant increment in hardness. The result shows the hardness improved by 35.77% and 77.8% for as-cast and heat-treated composites, respectively, compared to A356 alloy.

Microstructure and properties of in situ Al2O3 particle-reinforced aluminium alloy lattice rods fabricated by wire-arc-directed energy deposition

Lattice structures have great potential for application in the thermal protection systems of high-performance hypersonic vehicles (Mach > 5). They are lightweight, highly load-bearing and provide good heat insulation. Wire-arc directed energy deposition (WA-DED) is an effective method for preparing lattice structures made from metal lattice rods. A method is proposed to improve the ultimate tensile and compressive strengths of aluminium (Al) alloy lattice rods and lattice structures made by WA-DED. The replacement reaction of Al and NiO generates Al2O3, which was used to improve an Al–Cu alloy (2xxx series). An Al–Cu–NiO system cored wire filled with NiO particles was developed as the raw material for studying WA-DED lattice rods. Then the rod was heat treatment. Tests show that the strength of in situ Al2O3-particle-reinforced Al alloy rods was 281 MPa, which is 13.9% higher than that of Al–Cu 2319 Al alloy deposited rods. Reinforcement also increased the elongation (EL) from 11.3% to 13.5%. Strength is increased by Al and NiO reacting in situ to form an Al2O3 phase with refined grains. Most of the generated Ni is dissolved in Al2Cu to form a nano γ-Al7Cu4Ni phase, which plays a second-phase strengthening role. After T6 heat treatment, the strength and EL of 2319-NiO-cored wire deposited rods was 441 MPa and 10.4%. Fine, needle-like θ’-Al2Cu structures and Al2O3 and γ-Al7Cu4Ni nanoparticles pin dislocations, prevent their movement and improve the mechanical properties of the rod. The compressive strength of a planar lattice structure after T6 heat treatment was 105 MPa and its weight was only 15 g, demonstrating high specific strength. Finally, arc additive manufacturing with the developed 2319-NiO-cored wire was used to fabricate a curved-generatrix-shell pyramid lattice structure for use in the thermal protection cone of a hypersonic vehicle. Its thermal insulation coefficient was 82.5%, demonstrating excellent insulation performance. This study provides insights into the manufacturing of thermal protection systems for lightweight, high-strength and high-heat hypersonic vehicles.

Simultaneous refinement of α-Al and modification of Si in Al–Si alloy achieved via the addition of Y and Zr

Due to the Si/Zr-poisoning effect, conventional refiners often yield unsatisfactory results in refining α-Al grains for Al–Si alloys. In this work, the refinement of α-Al grains and the modification of eutectic Si are simultaneously achieved through the combined addition of Y and Zr to A356 alloy. The results indicate that the individual addition of Zr aids in refinement due to the formation of heterogeneous nuclei Al3Zr, while Y alone can refine α-Al grains and modify eutectic Si to a certain extent. When Y and Zr are added together, not only is the size of α-Al grains further refined to 22.1 μm, but the morphology of eutectic Si is also completely transformed into a fibrous structure. The interaction between Zr and Y decreases their solubility in the matrix, enhances heterogeneous nucleation, and induces the formation of a Al8FeMg3Si6YxZry phase enriched at grain boundaries, suppressing the growth of eutectic Si flakes. Compared to the use of Al–Ti–B refiners and Sr modifiers, the alloy with 0.25Zr and 0.3Y additions exhibits more significant grain refinement and Si modification. Furthermore, it facilitates the precipitation of fine Al3(Y, Zr) particles during the T6 heat treatment process, resulting in an optimal ultimate tensile strength (UST) of 289 MPa and an elongation of 9.75%.

Additive manufacturing of WE43 and modified AZ91D magnesium alloys using the laser engineered net shaping process

Magnesium alloys WE43 and AZ91D offer weight savings for structural applications. WE43 contains rare-earth elements such as yttrium and neodymium, whereas AZ91D and the AZ class of alloys are lower-cost containing aluminium and zinc. This work uses a modified version of the latter, identified as AZ91D*, where calcium and yttrium have been added. Laser Engineered Net Shaping (LENS) equipment was used to investigate the 3D printing behaviour of gas-atomized WE43 and AZ91D* material. Process evaluations were first done using single track laser scans across wrought substrates of WE43 and AZ31. Process parameters were then developed that enabled deposition of build coupons with less than 1% porosity. These were used for microstructural and mechanical property assessments. The energy densities used were in the range of 40 – 60 J/mm² for AZ91D*, while for WE43 a value of 50 J/mm² was selected. A focus of the work was managing the tendency of magnesium materials to fume heavily during deposition, while achieving a deposit with close to nominal density, i.e. having a low incidence of voids or other micro- or macro-structural defects. The porosity of AZ91D* builds did not seem to correlate with increasing deposition energy density, however WE43 builds did, up to a practical limit imposed by generation of excessive fume. WE43 generated much less fume than AZ91D*. Analysis of the input powder materials indicate the presence of oxides on the particle surfaces. The WE43 powders had a noticeable shell of yttrium oxide. The microstructures of WE43 builds show the presence of arc-shaped structures that are likely the same yttrium oxides, partially, or fully ‘unfolded’. Tensile testing was conducted on WE43 build coupons to assess the effect of a T6 heat treatment. The effect on the ultimate tensile and yield strengths was negligible, however the % elongation at break almost doubled. Inspection of the fracture surfaces suggests this was due to a change in mechanism from fracture initiation at sites of lack-of-fusion/un-melted particles, to a more ductile micro-void coalescence. Furthermore, a not previously described microstructure anomaly was observed: the presence of pure elemental magnesium crystallites and films on the fracture surface. These are attributed to condensation of magnesium vapour on previously built layers and are a possible reason for the existence of lack-of-fusion defects. The in-depth study of process fundamentals will enable future work on process fume inhibition based on process optimization and alloy composition with the goal of producing parts for biomedical and lightweighting applications.

Combined Effect of Particle Reinforcement and T6 Heat Treatment on the Compressive Deformation Behavior of an A357 Aluminum Alloy at Room Temperature and at 350 °C

Solid state sintering of cast aluminum powders by resistance heating sintering (RHS), also known as spark plasma sintering or field-assisted sintering technique, creates a very fine microstructure in the bulk material. This leads to high performance material properties with an improved strength and ductility compared to conventional production routes of the same alloys. In this study, the mechanical behavior of an RHS-sintered age-hardenable A357 (AlSi7Mg0.6) cast alloy and a SiCp/A357 aluminum matrix composite (AMC) was investigated. Aiming for high strength and good wear behavior in tribological applications, the AMC was reinforced with a high particle content (35 vol.%) of a coarse particle fraction (d50 = 21 µm). Afterwards, separated and combined effects of particle reinforcement and heat treatment were studied under compressive load both at room temperature and at 350 °C. At room temperature compression, the strengthening effect of precipitation hardening was about twice as high as that for the particle reinforcement, despite the high particle content. At elevated temperatures, the compressive deformation behavior was characterized by simultaneously occurring temperature-activated recovery, recrystallisation and precipitation processes. The occurrence and interaction of these processes was significantly affected by the initial material condition. Moreover, a rearrangement of the SiC reinforcement particles was detected after hot deformation. This rearrangement lead to a homogenized dispersion of the reinforcement phase without considerable particle fragmentation, which offers the potential for secondary thermo-mechanical processing of highly reinforced AMCs.

Effect of local loading on microstructure and enhanced mechanical property of large complex castings prepared by Al–Si–Fe–Mn–Mg–Cu alloy during squeeze casting

Flywheel shells with a complex structure and large wall-thickness difference, as key components in heavy trucks, serve to connect the engine and transmission. Formability and mechanical performance control of such components should be taken into consideration. In this work, an Al–Si–Fe–Mn–Mg–Cu alloy was used to manufacture the flywheel shell via squeeze casting. The role of local loading on microstructure and mechanical property at thick-walled positions was investigated. Furthermore, the effect of the squeeze casting specific pressure and heat treatment on the microstructure and mechanical property of the Al–Si–Fe–Mn–Mg–Cu alloy flywheel shells was also analyzed. The results showed that at the thick-walled positions, local loading not only helped eliminate the solidification defects, but also refined the microstructure including α-Al grains and secondary dendrite arm spacing. With increasing the squeeze casting specific pressure from 24 MPa to 32 MPa, microstructure refinement and mechanical property enhancement of squeeze casting flywheel shells were obtained. After T6 heat treatment, the yield strength and ultimate tensile strength of flywheel shells were further increased to 261.8 and 318.4 MPa, respectively, owing to the formation of spherical eutectic Si phases and nano-sized β'', Q and S precipitates.

Enhanced Plastic Stability: Achieving High Performance in a Al6xxx Alloy Fabricated by Additive Manufacturing.

Additive manufacturing (AM) facilitates the creation of materials with unique microstructural features and distinctive phenomena as compared to conventional manufacturing methods. Among the various well-fabricated AM alloys, aluminum alloys garner substantial attention due to their extensive applications in the automotive and aerospace industries. In this work, an Al6xxx alloy is successfully fabricated with outstanding performance. A nucleation agent is introduced to diminish the susceptibility to cracking during the AM process, thereby inducing a heterogeneous microstructure in this alloy. However, the introduction of ultrafine grains induces plastic instability, evidenced by the presence of Lüders band. This work investigates the evolution of the Lüders band and the strategy to reduce their undesirable effect. The heterogeneity destabilizes the band propagation and thus deteriorates the ductility. Through a T6 heat treatment, the local Lüders strain decreases from 10.0% to 6.2%, leading to a substantial enhancement in plastic stability. With the increase in grain growth and the enlargement of coarse grain regions, the mismatch between the local and macroscopic Lüders strain disappears. Importantly, the strength and the thermal conductivity are concurrently increased. The findings demonstrate the significance of ensuring plastic stability to achieve improved strength-ductility trade-off in AM alloys with heterogeneous microstructures.

Influence of Y Content and T6 Heat Treatment on the Organization and Mechanical Properties of Cast A356 Aluminum Alloy

The effect of Y content on the microstructure of A356 aluminum alloy and the mechanical properties of the alloy under T6 heat treatment was investigated. The results show that with the addition of 0.3 wt.% rare earth Y, the grain size of the cast A356 aluminum alloy reaches a minimum and the mechanical properties reach an optimum. After the T6 heat treatment, the grain structure of the alloy was further reduced and the mechanical properties were further improved. Compared to the cast A356 aluminum alloy without Y, the average α-Al grain size is reduced by 53.4%, the secondary dendrite SDAS by 32.2% and the average length of eutectic Si particles by 82.0%. The ultimate tensile strength (UTS) and elongation (El) increased to 280.75 MPa and 14.43% respectively, and the Vickers hardness increased to 102.9 HV.

Towards high performance Al–Si–Fe alloy castings via rheo-diecasting: Effect of injection velocity and heat treatment on microstructure evolution and property

The mechanical properties and thermal conductivity of Al–Si–Fe castings must meet high requirements in the automobile, aerospace, and communication fields. Traditional high-pressure diecasting (HPDC) castings often have dendritic structures and pore defects that deteriorate their overall performance. Therefore, an advanced rheo-diecasting (RDC) technique assisted by a vibrating contraction sloping plate was proposed to address this problem. However, the process optimization strategy, microstructural evolution, and performance improvement mechanisms remain unclear. The influence of the injection velocity on the microstructure, mechanical properties, and thermal conductivity of the RDC tensile specimens was first investigated. A high-performance cover plate was fabricated via RDC using an optimized injection velocity. The results showed that when the injection velocity increased to 2.8 m/s, the porosity decreased to a minimum value, and the mechanical performance and thermal conductivity of the RDC tensile specimens reached their maximum values. Furthermore, spherical eutectic Si phases and nanosized Mg2Si precipitates for the RDC cover plate were observed after T6 heat treatment, which further improved the mechanical properties and thermal conductivity owing to Orowan strengthening and decreased lattice distortion, respectively. The ultimate tensile strength, yield strength, elongation, and thermal conductivity for the RDC cover plate were 358.2 MPa, 279.9 MPa, 12.5%, and 180.72 W/(m·K), respectively, which were higher than that of reported similar alloys. From engineering perspectives, this study had the application value for produce of high-quality RDC castings.

Exfoliation behavior of EN AW 7020 with T6, step aging and ultrasonic impact peening processes

Abstract In this study the effect of T6 heat treatment, two-step aging treatment and ultrasonic impact peening on the exfoliation corrosion behavior of welded EN AW 7020 was investigated. Exfoliation tests were performed according to the ASTM G34-01 standard. As expected, as a result of the tests, the base material region of all three samples were showed better corrosion resistance than the heat-affected region. Ultrasonic impact peening and two-step aging treatment was observed that improved EXCO sensitivity in the weld area. When sorting was made by considering the resistance to corrosion of the heat affected zone of the samples, it was observed that the best resistance was shown by the sample with two-step aging treatment, and the worst resistance was shown by the sample with T6 heat treatment.

Liquid-phase diffusion bonding of Al alloy for casting using formate coated insert sheet

Liquid-phase diffusion bonding was performed in air at a bonding temperature of 400 °C, a bonding pressure of 20 MPa, and a heat holding time of 15 min. The specimens for liquid-phase diffusion bonding were AC2C and ADC12, aluminum alloy for casting. After liquid-phase diffusion bonding, solution annealing and aging treatments were also performed on the joints. As a result, the joint strength was improved by about 2 times and the joint efficiency was 90% by using the 3-layer insert material as compared with the Zn single-layer insert material. This was because the Si concentration in the liquid phase decreased by using the 3-layer insert material and Si was discharged to the outer circumference of the joint. By using the 3-layer insert material, the interfacial fracture factor after T6 heat treatment changed from Si particles to Mg oxides.

Effect of Mn/Ag Ratio on Microstructure and Mechanical Properties of Heat-Resistant Al-Cu Alloys.

This paper mainly investigated the effect of the Mn/Ag ratio on the microstructure and room temperature and high-temperature (350 °C) tensile mechanical properties of the as-cast and heat-treated Al-6Cu-xMn-yAg (x + y = 0.8, wt.%) alloys. The as-cast alloy has α-Al, Al2Cu, and a small amount of Al7Cu2 (Fe, Mn) and Al20Cu2 (Mn, Fe)3 phases. After T6 heat treatment, a massive dispersive and fine θ'-Al2Cu phase (100~400 nm) is precipitated from the matrix. The Mn/Ag ratio influences the quantity and size of the precipitates; when the Mn/Ag ratio is 1:1, the θ'-Al2Cu precipitation quantity reaches the highest and smallest. Compared with the as-cast alloy, the tensile strength of the heat-treated alloy at room temperature and high temperature is greatly improved. The strengthening effect of the alloy is mainly attributed to the nanoparticles precipitated from the matrix. The Mn/Ag ratio also affects the high-temperature tensile mechanical properties of the alloy. The high-temperature tensile strength of the alloy with a 1:1 Mn/Ag ratio is the highest, reaching 135.89 MPa, 42.95% higher than that of the as-cast alloy. The analysis shows that a synergistic effect between Mn and Ag elements can promote the precipitation and refinement of the θ'-Al2Cu phase, and there is an optimal ratio (1:1) that obtains the lowest interfacial energy for co-segregation of Mn and Ag at the θ'/Al interface that makes θ'-Al2Cu have the best resistance to coarsening.

Development of an Alternative Heat Treatment to the Traditional T6 Heat Treatment of AlSi10Mg Alloy Produced by Additive Manufacturing

Development of an Alternative Heat Treatment to the Traditional T6 Heat Treatment of AlSi10Mg Alloy Produced by Additive Manufacturing

Innovative local shear forming method for enhanced formability of tubular parts with high stiffened ribs

Large-sized thin-walled tubular parts with high stiffened ribs are key lightweight structural components used in transportation. To address the challenges of integral forming, a novel local shear forming (LSF) technique that combines the advantages of spinning and shear forging (SFG) is proposed. Finite element (FE) simulations and experimental work have revealed the distinct deformation mechanisms of local shear forming in contrast to those of conventional shear forging or spinning. During local shear forming, the surface material of the billet undergoes sequentially axial upsetting deformation, primary shear deformation, reverse shear deformation, circumferential tensile deformation and radial displacement to form the rib. Gradient plastic deformation is observed through the thickness of the formed wall rather than near the wall surface. The effects of local loading include reduction of the secondary shear deformation zone, reduction of circumferential constraint in the loading zone, material circumferential transfer, and expansion-shrinkage deformation of the billet. The former two decrease the rib thickness and promote radial transfer of the material. The latter two result in a significant strengthening of the formed rib and wall. Moreover, tearing and buckling are suppressed, which enhances the relative wedge thickness up to 50 % of the wall thickness of the billet. The aspect ratio of the formed rib can be as high as 3 for the high strength 2A12 alloy and 6 for the highly ductile 1A30 alloy. Shear deformation in the rib promotes recrystallization in the subsequent T6 heat treatment and refines the microstructure. Corrosion resistance is not degraded though microstructural change. Local shear forming shows good potential for forming tubular parts with an external rib structure.

Squeeze casting of 4032 aluminum alloy and the synergetic enhancement of strength and ductility via Al-Ti-Nb-B grain refiner

The 4032 aluminum alloy is a high-Si deformation aluminum alloy, that is commonly generated through forging due to the difficulties involved in its direct casting. In this work, the 4032 aluminum alloy is innovatively prepared via a squeeze casting process, and the Al-6Nb-1.5Ti-0.5B refining agent is incorporated to enhance its mechanical properties. A range of analytical techniques are subsequently employed to analyze the grain refinement mechanism of Al-6Nb-1.5Ti-0.5B under squeeze casting conditions. It was found that the microstructure of the aged 4032 aluminum alloy after refinement treatment was mainly composed of α-Al grains measuring <100 μm in size, in addition to a eutectic Si phase, that is accompanied by stacked dislocations and diffusely distributed Q′-Al5Cu2Mg8Si6 and θ′-Al2Cu phases. The yield strength of the alloy reached 340 MPa, its tensile strength was 404 MPa, and the elongation was 4.1 %. In the presence of the Al-6Nb-1.5Ti-0.5B refiner, the generation of nucleation cores (e.g., MAl3(M = Ti, Nb)) in the melt led to a significant reduction (∼50 %) in the α-Al grain size of the aged 4032 aluminum alloy (i.e., 95.1 ± 21.0 μm), compared with the standard alloy. After the T6 heat treatment of the refined 4032 aluminum alloy, the size of the precipitation phase was reduced by 36.8 %, and fine silicon particles with a spherical morphology and a more random distribution were observed. No obvious selective orientation was detected, and the fracture morphology improved significantly, thereby leading to a synergistic improvement in the strength and toughness of the alloy.

Effects of Heat-Treatment and Cold-Rolling on Mechanical Properties and Impact Failure Resistance of New Al 6082 Aluminum Alloy by Continuous Casting Direct Rolling Process.

Al 6082 aluminum alloy has excellent corrosion resistance, strength, and formability. However, owing to the recrystallization effect of a hot working process, coarse grains form easily in this material, which reduces its strength and service life. The novel continuous casting direct rolling (CCDR) method can prevent the deterioration of this material. Thus, we used CCDR Al 6082 aluminum alloy as the research material in this study. By subjecting a CCDR Al 6082 aluminum alloy to heat treatment (T4 and T6) and cold rolling, the influence of recrystallization effect on its mechanical properties and on impact failure resistance were explored. The results demonstrated that the specimen subjected to T4 heat treatment had a higher elongation and that the specimen subjected to T6 heat treatment had a higher strength. After cold rolling, the hardness and strength of the specimens subjected to different heat treatments (coded T4R4 and T6R4) increased because of the work's hardening effect. Moreover, the elongations of both specimens decreased, but they were higher than the industrial standard (>10%). The strength of specimen T6R4 was higher (up to 400 MPa) than specimen T4R4. Moreover, relative to specimen T4R4, specimen T6R4 had greater tensile and Charpy impact failure toughness.

Thick Film Sensor Manufacturing Techniques for Realization of Smart Components via Low Pressure Die Casting

Recent developments like autonomous driving have increased the interest of the automotive industry in structural health and condition monitoring of safety-relevant components often manufactured via High or Low Pressure Die Casting (HPDC, LPDC). Specifically the latter process is important in this field as the improved quality of castings produced facilitates T6 heat treatments aimed at optimizing mechanical performance of such components. The specific challenge associated with this approach is that it produces critical thermal loads which may compromise the characteristics of the integrated sensor. The present study shows the results obtained by LPDC on thick film sensor systems prepared by means of screen printing on aluminum substrates. The response of the sensor systems to the thermal loads associated with the casting process is evaluated in casting experiments, with temperatures reached during casting checked by means of thermocouples attached to the inserts. The focus is on the influence on general properties of the piezoresistive sensors as well as on their response to thermal and mechanical stimuli. The results show that in contrast to HPDC, in the case of LPDC, the former provides stimuli for thermally induced processes which can compromise sensor layers. The respective trends have been studied via resistance measurements on samples subjected to repeated firing cycles and actual casting experiments.

Microstructure evolution and mechanical properties of Al-12Si-xCu-yNi-1Mg alloy with different Ni/Cu ratios

High-temperature properties are the key factor affecting the industrial application of cast Al-Si alloy. In this paper, four kinds of Al-12Si-xCu-yNi-1Mg (y = 7.5-x, x:4.84, 5.17, 5.55, 6.00.) alloys were prepared by changing the Ni/Cu ratio and regulating the type and proportion of the heat-resistant phase, and then systematically analyzed the changing of microstructure and mechanical properties and clarified the heat resistance mechanism of the alloy. The experimental results show that with the increase of the Ni/Cu ratio, the eutectic Si phase of the as-cast alloys was refined, the blocky Al2Cu phase and the strip Al7Cu4Ni phase disappeared, and the reticular Al3CuNi heat-resistant phase increased, and the size of Al3CuNi phase decreases first and then increases. After T6 heat treatment, the eutectic silicon spheroidized, and the nickel-rich phase did not change significantly. As the Ni/Cu ratio increases, the tensile strength of the alloy at room temperature increases first and then decreases, and its tensile strength at high temperature increases continuously. When the Ni/Cu ratio is 0.45, and the maximum value of tensile strength at room temperature is 355 MPa. When the Ni/Cu ratio is 0.55, the content of the Al3CuNi phase with high thermal stability is most, and the Al2Cu phase with poor stability is less, so the high-temperature tensile strength is the highest, and the value of tensile strength at 275 °C, 325 °C and 375 °C is 192 MPa, 172 MPa, and 89 MPa, respectively.