Ti-6Al-4V, also known as Grade 5 titanium or titanium alloy 6-4, is one of the most widely specified titanium alloys for high-strength, lightweight, corrosion-resistant components. For engineers, sourcing teams, and CNC machining buyers, the key question is not simply whether the alloy is strong. The real question is whether its strength, cost, machinability, surface behavior, and inspection requirements match the part design. This article explains the alloy from a manufacturing point of view, including composition, properties, applications, CNC machining strategy, comparison with Grade 2 titanium, finishing options, and common design decisions.
Ti-6Al-4Vとは何ですか？
Before choosing a titanium material, it helps to understand why Ti-6Al-4V became the default alloy for many demanding projects. It is not pure titanium. It is an alpha-beta titanium alloy designed to combine the corrosion resistance of titanium with much higher mechanical strength.
簡単に説明するグレード5チタン
Grade 5 titanium is the common commercial name for Ti-6Al-4V. The name describes its main alloying elements: about 6% aluminum and 4% vanadium, with titanium as the balance. Aluminum helps stabilize the alpha phase and contributes to strength, while vanadium helps stabilize the beta phase and improves heat-treatment response. This alpha-beta structure is why the alloy can be strengthened more effectively than commercially pure titanium grades.
なぜ「主力合金」と呼ばれるのか
The alloy is popular because it delivers a rare balance: high strength-to-weight ratio, useful fatigue performance, broad corrosion resistance, and availability in bar, plate, sheet, forged stock, and additively manufactured feedstock. For CNC machined titanium parts, this means designers can reduce weight without moving to a very exotic alloy. It is commonly selected when aluminum is too soft or too weak, and stainless steel is too heavy.
このガイドが価値を提供するポイント
Many material pages stop at datasheet values. In real manufacturing, however, Ti-6Al-4V also raises questions about tapping, tool wear, pocketing strategy, spring passes, surface galling, and whether Grade 2 titanium might be easier to machine. This guide connects the datasheet to CNCmachining decisions so the alloy can be specified with fewer surprises.
Ti-6Al-4V Chemical Composition and Material Identity
The composition of Ti-6Al-4V looks simple, but small differences in oxygen, iron, hydrogen, and processing condition can affect ductility, fracture toughness, and machining behavior. When quoting precision CNC parts, the grade, standard, and heat condition should be treated as part of the specification, not as optional details.
典型的な組成範囲
The table below summarizes the typical composition range used for Grade 5 titanium. Exact limits depend on the governing specification, product form, and certification requirements, so the purchase order should always reference the required standard when traceability matters.
| 要素 | 典型的な範囲または限界 | 製造上の重要性 |
| チタン | バランス、約87.6～91% | Base metal that forms a stable oxide film for corrosion resistance |
| アルミニウム | 5.5-6.75% | Improves strength and stabilizes the alpha phase |
| バナジウム | 3.5-4.5% | Supports beta phase stability and heat-treatment response |
| 鉄 | 通常、最大0.25～0.40%に制限される | Can influence strength, ductility, and certification requirements |
| 酸素 | 通常、最大約0.20%に制限される | Higher oxygen raises strength but reduces ductility |
| 炭素、窒素、水素 | 残留物の低限値 | Important for toughness and process reliability |
グレード5とグレード23 ELIの比較
A common source of confusion is the difference between Grade 5 and Grade 23. Grade 23 is often described as Ti-6Al-4V ELI, where ELI means extra low interstitial. The chemistry is similar, but oxygen and iron are held lower. This usually improves ductility and fracture toughness while slightly reducing strength. For general CNC machined industrial components, Grade 5 is often sufficient. For fracture-critical or highly regulated applications, Grade 23 may be specified.
確認すべき規格名称
Common references include UNS R56400 for Grade 5 and product standards such as ASTM B265 for sheet or plate and ASTM B348 for bar. Aerospace and high-reliability projects may call out AMS specifications. A drawing that only says “titanium” is not precise enough for procurement, machining planning, or inspection.
Mechanical and Physical Properties That Matter in Design
The value of Ti-6Al-4V comes from more than one number. Designers often focus on tensile strength, but density, stiffness, fatigue behavior, thermal conductivity, hardness, and elongation all affect how a part performs and how it should be machined.
強度、密度、剛性
Ti-6Al-4V has a density around 4.43 g/cm3, which is much lower than stainless steel and nickel alloys. Its elastic modulus is roughly 105-120 GPa, lower than steel but higher than aluminum. This combination makes the alloy attractive for lightweight structural components, but it also means thin walls can deflect during machining if workholding and tool pressure are not controlled.
| 特性 | 典型的値 | 設計上の意味 |
| 密度 | 約4.43 g/cm³ | Useful for weight reduction compared with steel |
| 引張強度（極限値） | About 895 MPa minimum; higher in some heat-treated conditions | コンパクトで高荷重な部品を支える |
| 降伏強度 | About 828 MPa minimum; condition dependent | Important for brackets, housings, and loaded features |
| 弾性係数 | 約105～120 GPa | Stiffer than aluminum but less stiff than steel |
| 伸び率 | Often 10% or higher, depending on condition | Affects formability and fracture behavior |
| 熱伝導率 | 約6.6～7.2 W/mK | Heat stays near the cutting edge during machining |
疲労特性と使用温度範囲
The alloy is often chosen for parts that see repeated loading because it offers useful fatigue resistance when properly processed and finished. It is also commonly used at moderate elevated temperatures, often referenced up to about 400°C for many applications. However, fatigue performance depends heavily on surface condition, notches, residual stress, and environment. A sharp internal corner or poor surface finish can erase much of the benefit of a strong alloy.
Why Datasheet Values Are Not the Whole Story
Properties vary with annealed, solution-treated, aged, forged, wrought, or additively manufactured condition. For CNC parts, the most important step is to match the drawing requirement to a real mill certificate and an achievable machining plan. Over-specifying strength may increase material cost and tool wear without improving the actual part.
Corrosion Resistance, Wear Behavior, and Surface Finish
Titanium alloys are often described as corrosion resistant, but Ti-6Al-4V should not be treated as a universal solution for every chemical environment. Its passive oxide layer is strong in many conditions, yet surface wear and sliding contact require extra attention.
Corrosion Behavior in Common Environments
Ti-6Al-4V performs well in seawater, many chloride environments, and many oxidizing conditions because a thin oxide layer forms naturally on the surface. That oxide layer is the reason titanium can remain stable where many other metals corrode. In strongly reducing acids or very aggressive chemical media, however, commercially pure titanium grades or modified titanium grades may be more suitable.
摩耗、ガリング、接触面について
A frequent misunderstanding is that high strength automatically means high wear resistance. Ti-6Al-4V has relatively poor sliding wear behavior compared with hardened steels or coated materials. When titanium slides against titanium or other metals under load, galling and material transfer can occur. For moving interfaces, designers should consider coatings, surface hardening, bushings, inserts, lubrication, or a mating material with better tribological compatibility.
CNC加工部品の表面仕上げオプション
As-machined finish is common for prototypes and functional internal features. Bead blasting can create a uniform matte appearance, while polishing can improve cosmetic surfaces but may raise cost. Passivation or controlled cleaning may be required when the part must be free of embedded contamination. For wear-sensitive surfaces, nitriding, oxidation-based treatments, or physical vapor deposition coatings may be considered after confirming dimensional impact.
| 表面仕上げの要求事項 | 可能なアプローチ | 注意事項 |
| 外観上のマットな質感 | ビードブラスト | Protect critical threads and precision bores |
| 清掃性の向上 | 精密加工と管理された洗浄 | 埋め込まれた研磨媒体の混入を避ける |
| 低い摺動摩耗 | コーティングまたは表面硬化処理 | 厚さと密着性の検証 |
| 密閉性の高いシール面 | 仕上げ加工やラップ加工 | 平面度と加工痕の管理 |
Common Product Forms, Standards, and Sourcing Considerations
A good Ti-6Al-4V quote starts before machining begins. Product form, grain direction, stock condition, and certification level can change lead time, cost, and quality risk. The same alloy name can arrive as bar, plate, sheet, forging, or additive stock, and each form behaves slightly differently.
棒材、板、シート、鍛造材の在庫
Round bar is common for turned parts, shafts, spacers, and threaded components. Plate is common for brackets, housings, frames, and milled structural parts. Sheet is used for formed or thin machined components. Forged stock may be selected when directional properties, fatigue strength, or high-integrity structure are critical. The correct choice depends on part geometry and the final property requirement.
トレーサビリティと製造所証明書
For aerospace, medical, energy, and high-value industrial projects, the material certificate is not just paperwork. It confirms grade, heat number, chemical composition, mechanical properties, product form, and sometimes heat treatment. When CNC machining Ti-6Al-4V, traceability also helps resolve unexpected issues such as variable tool life, inconsistent burr formation, or unexplained dimensional movement.
調達におけるコスト要因
Ti-6Al-4V is more expensive than common aluminum alloys and many steels because titanium extraction, melting, processing, and certification are demanding. Cost also rises when the part requires oversize plate, extra low interstitial chemistry, special testing, or small-quantity purchase. A design-for-manufacturing review can often reduce cost by choosing standard stock thicknesses, avoiding unnecessary deep cavities, and allowing realistic radii.
Ti-6Al-4Vが使用される場所
Ti-6Al-4V appears in many industries because it solves the same basic problem in different ways: it provides high strength without excessive weight and resists corrosion in environments where ordinary metals may struggle. The best applications use both advantages, not just one.
Aerospace, Robotics, and Performance Hardware
In aerospace and performance equipment, the alloy is used for brackets, frames, compressor-related parts, fasteners, linkages, and structural hardware where low weight and high strength are valuable. In robotics and automation, it can be used for lightweight arms, grippers, and moving assemblies when aluminum lacks stiffness or wear margin and stainless steel adds too much mass.
医療、海洋、化学機器用途
Medical applications often use titanium alloys because of biocompatibility, corrosion resistance, and strength. Marine and chemical equipment use Ti-6Al-4V when corrosion resistance and mechanical strength are both required. However, the alloy should still be checked against the actual fluid, temperature, cleaning process, and contact materials. For some highly corrosive environments, another titanium grade may be more cost-effective or more resistant.
選択を避けるべき場合
Ti-6Al-4V is not the best answer for every lightweight part. If the component carries low load and does not face corrosion or temperature challenges, 6061 or 7075 aluminum may be more economical. If the part is mainly a sliding wear component, a coated steel, bearing bronze alternative, or engineered polymer may perform better. If formability is more important than strength, commercially pure titanium may be easier to process.
CNC Machining Ti-6Al-4V: Introduction and Core Strategy
Ti-6Al-4V is very common in CNC machining, but it is not a “set it and forget it” material. It rewards rigid setups, sharp tools, controlled heat, and stable chip formation. The central machining challenge is that the alloy is strong, springy, and a poor conductor of heat, so heat and stress stay close to the tool edge.
Why Titanium Feels Different from Aluminum or Stainless Steel
Compared with aluminum, Ti-6Al-4V has much higher strength and lower thermal conductivity. Compared with many stainless steels, it may feel more elastic and less forgiving when the tool rubs instead of cuts. If the edge dulls, temperature rises quickly, the surface can work harden locally, and tool life can collapse. This is why titanium machining guidance often emphasizes low surface speed, positive geometry, and abundant coolant.
一般的なフライス加工と旋削の原則
Successful CNC machining normally starts with carbide tools, rigid holders, short tool overhang, strong coolant delivery, and cutting parameters that keep the tool engaged without rubbing. Many shops use lower surface speeds than they would for steel, moderate to strong feed per tooth, and toolpaths that avoid burying the cutter. Trochoidal or adaptive milling can help maintain consistent chip load in pockets and reduce heat spikes.
Tapping, Thread Milling, and Deep Features
Small threaded holes in Ti-6Al-4V deserve special planning. Conventional tapping can break tools if the tap is not designed for titanium, if the thread percentage is too high, or if chips pack in the hole. Thread milling is often safer for expensive parts because it lowers cutting force, improves chip evacuation, and can recover from tool wear more gracefully. Deep pockets also need attention because tool deflection and heat accumulation can cause tapered walls, poor floor finish, and corner overcut.
| 加工上の課題 | 典型的な原因 | より優れた制御方法 |
| 工具の急速な摩耗 | 切削刃先に熱が集中する | Use sharp carbide, coolant, conservative surface speed |
| ねじの信頼性の低さ | 高いトルクと切りくずの詰まり | Use thread milling or titanium-specific taps |
| 壁面のテーパーまたは振動 | 弾性変形と長尺工具の使用 | Use rigid setup, rough/finish strategy, spring pass |
| エッジ部のバリ | 延性のある切りくずの流れと工具の摩耗 | エッジブレイクやバリ取りの計画 |
| 熱による変色 | 冷却液不足や摩擦による影響 | Improve coolant aim and maintain chip load |
Ti-6Al-4V vs Grade 2 Titanium CNC Machinability
When people compare titanium grades for CNC parts, the most useful comparison is often Ti-6Al-4V versus Grade 2 titanium. Grade 2 is commercially pure titanium, while Grade 5 is alloyed for higher strength. Both are corrosion resistant, but they cut differently and fit different part requirements.
強度と切削力の違い
Grade 5 titanium is significantly stronger than Grade 2, so it usually requires more cutting force and more careful heat control. Grade 2 is softer and more ductile, which can make it easier in some operations but also more prone to gummy chip behavior. Ti-6Al-4V is more likely to punish dull tools, heavy rubbing, and poor coolant delivery. Grade 2 may be easier for simple corrosion-resistant parts where high strength is not needed.
どちらがより加工しやすいか？
There is no universal answer because toolpath, feature geometry, and stock condition matter. For many precision CNC shops, Grade 2 is easier from a cutting-force perspective, while Ti-6Al-4V is more predictable for high-strength structural components if the process is well controlled. Grade 5 often needs tighter discipline: sharp carbide tools, reliable coolant, stable fixturing, and planned finishing passes. Grade 2 may allow gentler machining but can still create burrs and stringy chips.
CNC購入者向け選定表
Use the comparison below as a first-pass selection guide. It does not replace a drawing review, but it helps clarify why one titanium grade may be better than another for a specific CNC machined part.
| 質問 | Ti-6Al-4V グレード5 | グレード2チタン |
| 高い強度対重量比が必要ですか？ | ほとんどの場合に最適な選択 | 強度が低く、多くの場合理想的ではない |
| 最大限の延性／成形性が必要ですか？ | 中程度で条件次第 | 通常はより優れている |
| 単純な部品の加工を容易にしたいですか？ | より厳しい条件 | Often easier, but still not like aluminum |
| 強固なねじ部品が必要ですか？ | 正しいねじ加工戦略があれば良好 | 強度が低いとねじ負荷に制限が出る可能性 |
| Need corrosion resistance without high load? | 優れているが過剰仕様になることも | 多くの場合費用対効果の高い選択肢 |
Heat Treatment, Forming, and Fabrication Behavior
Ti-6Al-4V can be heat treated and fabricated, but the process window should be respected. The alloy responds to annealing, solution treatment, aging, forging, and forming, yet the chosen route must match the final property and dimensional requirements.
焼なましと応力除去
Annealing is commonly used to stabilize the microstructure, improve ductility, and reduce residual stress after prior processing. Stress relief can be valuable after heavy machining, especially when the part has thin walls, uneven stock removal, or tight flatness requirements. For CNC parts, stress relief is not always necessary, but it should be considered when the geometry encourages movement during or after machining.
固溶化処理と時効処理
Because Ti-6Al-4V is an alpha-beta alloy, it can be solution treated and aged to increase strength. However, higher strength can reduce machinability and ductility. If a part will be heat treated after machining, dimensions, distortion, surface oxidation, and final finishing allowances should be planned in advance. If the part is machined after heat treatment, tool life may be shorter and process control becomes more important.
成形および熱間加工に関する考慮事項
The alloy can be hot or cold formed, but it is less forgiving than commercially pure titanium. Hot forming can reduce springback and forming force, while cold forming may require larger radii and intermediate stress relief. For machined parts made from plate or bar, forming is often less important than residual stress and stock stability, but it still matters when the design combines formed and machined features.
Design for CNC Machining: Tolerances, Features, and Cost Control
The easiest way to reduce Ti-6Al-4V cost is not to ask the machine shop to “just run it slower.” Better results come from designing features that respect the material. The alloy can hold precision, but unnecessary sharp corners, deep pockets, tiny tapped holes, and thin walls all increase risk.
工具寿命を向上させる特徴設計
Internal corner radii should be as generous as the design allows because small tools deflect more and wear faster in titanium. Deep pockets should include tool access, chip clearance, and staged roughing. Thin walls should be supported by machining sequence, tabs, or temporary stock when possible. Tolerances should be tight only where function requires them, because every additional finish pass in Ti-6Al-4V adds time and tool cost.
ねじ、穴、エッジブレイク
Threaded holes should be reviewed for depth, pitch, and engagement percentage. In many titanium parts, thread milling offers better process security than tapping, especially for blind holes or expensive parts. Holes should have realistic depth-to-diameter ratios, and edge breaks should be specified clearly. Titanium burrs can be stubborn, so deburring should be planned rather than left as an afterthought.
検査と表面品質
Inspection should focus on the features that titanium machining can affect most: thread quality, bore roundness, wall straightness, flatness, and surface finish in high-stress areas. If the part will experience fatigue loading, avoid tool marks, sharp transitions, and uncontrolled scratches. A slightly higher machining cost for better surface control can be cheaper than a failure caused by a stress riser.
| 設計上の選択 | コストへの影響 | 推奨される加工方向 |
| 非常に小さな内径のR | 工具摩耗が高く、サイクルタイムが長くなる | 機能上許容される場合は大きなR角を使用 |
| 深いブラインドスレッド穴 | タップ破損リスクの高さ | Consider thread milling or shallower engagement |
| 薄い支持されていない壁 | たわみやびびりのリスク | 補強を追加するか公差を緩める |
| バリ取りの未指定 | 外観や適合性にばらつきが生じる | エッジ破損範囲の明示 |
| すべての面で美観的な仕上げを施す | 追加の仕上げ工程時間 | Limit cosmetic requirements to visible surfaces |
結論
Ti-6Al-4V is one of the most useful titanium alloys because it combines high strength, low density, corrosion resistance, and broad availability. Its value is highest when the part truly needs strength-to-weight performance, not just a premium material name.
最終的なまとめ
For CNC machined parts, success depends on sharp tools, coolant control, rigid setups, realistic feature design, and clear material specifications. Choose Grade 5 when strength matters; consider Grade 2 when corrosion resistance and easier processing matter more than load capacity.
選定時の注意点
The best titanium part starts with material choice, but it succeeds through manufacturable design.
FAQ
These questions summarize common concerns from engineers and sourcing teams before ordering Ti-6Al-4V CNC machined parts. The answers are intentionally direct so they can be used during early material selection and design review.
Is Ti-6Al-4V the same as Grade 5 titanium?
The answer depends on the final part function, but the general guidance is straightforward.
直接的な回答
Yes. Grade 5 titanium is the common name for Ti-6Al-4V. It contains aluminum and vanadium as the main alloying elements and is stronger than commercially pure titanium grades.
Ti-6Al-4Vは加工しにくいですか？
The answer depends on the final part function, but the general guidance is straightforward.
直接的な回答
Yes, it is more demanding than aluminum and many steels. The low thermal conductivity, high strength, and elastic behavior require sharp carbide tools, stable workholding, strong coolant, and careful feed and speed selection.
Ti-6Al-4Vはタップ加工できますか？
The answer depends on the final part function, but the general guidance is straightforward.
直接的な回答
Yes, but tapping should be planned carefully. Use tools intended for titanium, avoid excessive thread percentage, provide lubrication or coolant, and consider thread milling for blind holes, small threads, or high-value parts.
Ti-6Al-4Vには表面処理が必要ですか？
The answer depends on the final part function, but the general guidance is straightforward.
直接的な回答
Not always. Many parts work well as-machined or bead blasted. Surface treatment becomes important when the part needs better wear resistance, a controlled cosmetic finish, lower galling risk, or special cleaning requirements.
Is Ti-6Al-4V better than stainless steel?
The answer depends on the final part function, but the general guidance is straightforward.
直接的な回答
It depends on the goal. Ti-6Al-4V is much lighter and offers high strength, but stainless steel may be cheaper, easier to machine, stiffer, and better for some wear or high-temperature conditions.