Analysis: iPhone 6S May Use 6013 Aluminum Alloy Instead of 7000 Series Alloys

Apple, Inc. (AAPL) in recent years has seen a number of otherwise stellar mobile devices marred by embarassing hardware or software defects.  After suffering through “antennagate” in 2010 and the Maps debacle in 2012, some unlucky Apple fans experienced “bendgate” last year.  

I. Preventing Another Bendgate

With a relatively long ~6.22 in. (158.1 mm) aluminum unibody frame, the iPhone 6+’s frame had the potential to act as a lever in the user’s pocket, purse, or bookbag.  And with no hardened glass back plate and a razor thin 0.302 in. (7.1 mm) profile, the frame proved susceptible to bending.

Bending Bad — the story of one man who went too far with his iPhone. [Image Source: YouTube]
With the features and improvements of iOS 9 demoed at Apple’s 2015 Worldwide Developers Conference (WWDC) two weeks ago, the focus is shifting to what Apple is planning hardware-wise for its ninth generation flagship smartphone.

A new research note by Ming-Chi Kuo, an analyst at Taiwan’s second largest investment bank KGI Securities, claims to have the inside scoop on how Apple is going to prevent another bendgate.  According to the note, Apple is looking to make two crucial changes to strengthen the frame.

First, it will thicken the frame by approximately 1/128th of an inch (0.2 mm) — a small, but significant 2.8 percent increase in frame thickness (the frame also reportedly will be 0.0059 in. (0.15 mm ) longer).  The larger frame potentially kills two birds with one stone, by both adding sufficient room to incorporate Apple’s new pressure-sensitive “Force Touch” technology and in the process adding more metal to resist deformation.

Secondly, the report says that Apple will switch to a stronger aluminum alloy.

The report claims that Apple will switch to a 7000 series aluminum alloy.  My only skepticism lies in whether that’s truly the higher strength alloy Apple will select, although it’s certainly one route which it could go.  I would suspect it’s actually somewhat more likely that Apple will switch to a stronger 6000 series aluminum alloy.

Let’s look at what alloy Apple currently uses, what options it has, and where the rumor of the 7000 series aluminum alloy arose.

II. Metalhead

Apple has long been a fan of using aluminum in its body designs, a premium device design strategy that it largely acquired from Japan Sony Corp. (TYO:6758) in late 80s and over the course of the 90s (see the WM-DD9 (Walkman) casette deck (1989) for example).

While most mistake the iPod for Apple’s first aluminum product, the first few iPod generations actually used plastic frames with chrome-painted trim.  The first true aluminum body designs from Apple were the 12-inch PowerBook6 G4 and 17-inch PowerBook5 G4 laptops introduced in Jan. 2003.  

Fans dubbed these laptops with the affectionate nickname “AlBooks”, in homage to the aluminum skin that replaced the previous generation’s titanium body.  Since then aluminum crept into most of Apple’s other products, including the iMac (2007), iPod (2007), etc.

The first iPhone to use a metal frame was the iPhone 4 (2010), which replaced the plastic design of early generations with a stainless steel frame, with a hardened glass back face.  The iPhone 4S (2011) used a similar design.

The iPhone finally ditched the heavier stainless steel and received a lightweight aluminum skin in 2012 with the launch of the iPhone 5.  The iPhone 5 dropped most of the back glass of the iPhone 4S, but kept small hardened glass elements on the top and bottom of the backface, essentially sandwiching a layer of colorful anodized alumnium.  The iPhone 5S (2013) notably dropped the back glass, moving the iPhone to its current colorful anodized aluminum unibody design.
The iPhone 5 was the first iPhone to use a lightweight alloy aluminum frame.

The iPhone 5 reportedly used plain Aluminum 6061 — an alloy which metal firm Azom dubs “one of the most extensively used of the 6000 series aluminum alloys.”

Machining of the iPhone 5’s case is pictured.  The phone reportedly used aluminum alloy 6061.
The case is reportedly cut out and machined from extruded aluminum columns.  Once the frame is cut out of the aluminum block, color is applied via a Type II anodizing finish.  Type II anodization is easier to chip or scratch, but it also gives more vivid colors than the sturdier Type III anodization.

A scuffed iPhone 5 delivery is seen. [Image Source: The Verge]
In response to 2012 criticism over the metal frame of the iPhone 5 being susceptible to scratches and scuffs (the so-called “scuffgate”), Apple responded:
Any aluminum product may scratch or chip with use, exposing its natural silver color. That is normal.
PhoneArena claims that with the iPhone 6/6+ Apple upgraded to Aluminum 6063.  With the launch of the iPhone6/6+, Apple is said to have tapped Tainan City, Taiwan-based Catcher Technologies Comp., Ltd. (TPE:2474) to machine the unibody (source: an April 2014 Morgan Stanley (MS) research note).  Catcher’s product page offers 6063-T4 and 6063-T5 cast aluminum, so this makes sense.  It also makes sense given that 6063 alloys have heavily replaced 6061 in the U.S.  As retailer “TheAluminumSource” states:
The 6063 alloy is the most commonly used extrusion alloy in the US today.  It is our (unconfirmed) opinion that it probably accounts for about 75% – 80% (by weight) of all aluminum extrusions produced. For this and other reasons, it is also the cheapest alloy in terms of price per pound. It offers the additional benefits of being fairly easily machinable (though not the best for extensive machining), easily fabricated and welded, and comparatively strong (see our mechanical properties tables).
  It also anodizes well, including most common and specialty colors, and is a good strata for painting (as are most alloys). 6063 is used in countless applications, including most window – patio door – curtainwall – storefront – skylight architectural applications, many automotive and a few aircraft applications, some boating, sporting goods, and you – name – it other uses. It is found in wire, rod, bar, extrusions, structural shapes, tubing, pipe, etc.
GSMArena suggests [based on this Reddit discussion] that some iPhone 6S cases are also machined from the slightly different 6003 aluminum alloy.  Further adding to the mystery, Chinese aluminum supplier Shanghai Reliance Alu Co., Ltd. brags that since early 2014 it has been supplying “aluminum/aluminium extruded bar for iPhone/iPad/Airbook (RA-009)” (this material is available in several tempers, reportedly Apple is using the 6082-T6/T651 — the highest temper).

Anodizing allows Apple to add die to the aluminum alloys and guard them against corrosion (iPhone 5S is pictured).
It’s possible both claimed alloys may be accurate different batches of iPhone 6/6+ actually use different alloys.  In addition to Catcher, Apple contracted at least two other firms to machine the cases — Jabil Circuit, Inc. (JBL) and Foxconn Technology Comp., Ltd. (TPE:2354) [source].  Different suppliers may be using different alloys, albeit all are within some general neighborhood of each other strength-wise.

So Apple is likely using some assortment of 6003 (temper unknown); 6063-T4 or T5; 6082-T6/T651 aluminum alloy in its current gen devices.

III. 7000 Series Alloys Cometh?

So what’s next?

The KGI research note suggests the answer is in 7000 series aluminum.  Where does this claim come from?  It’s possible it’s heard some unique word from suppliers, but it may be basing this on the fact that Apple adopted 7000 series aluminum for the shell of the Apple Watch.

The Apple Watch’s product page describes:
For Apple Watch Sport, we started with 7000 Series aluminum — the same used in competition bicycles. We altered it to create a new alloy that’s just as light, yet even more durable — it’s 60 percent stronger than most aluminum, and one-third the density of stainless steel. It has a bright, lustrous colour and a uniform structure free of defects and impurities. Each case is machined and polished, then blasted with microscopic zirconia beads to achieve a consistent, satin texture. A special anodizing process creates a hard, clear outer layer that helps protect against scratches and corrosion.
However, while it is to be expected that Apple would seek out a stronger alloy after bendgate, there’s no definitive evidence that it will be a 7000 series alloy.  While it’s true that 7000 series alloys are generally more durable than 6000 series alloys, they’re also fundamentally different in their chemical composition.  6000 series alloys are doped with a combination of silicon and magnesium; 7000 series are doped primarily with zinc.  
Overview of chemistries and capabilities of aluminum alloy series [Image Source: Industrial Lasers]
The different chemical composition means that switching from a 6000 series alloy to a 7000 sereis alloy can bring additional complications.  Generally speaking, 7000 series alloys are much harder to machine and the machining process is more time consuming.  7000 series aluminum is also more expensive (as production volume is lower), is not fusion weldable (not necessarily an issue here, but worth mentioning) , and is more susceptible to corrosion [source].  Machinability is similar for the two alloys, but 7000 series alloys have shown themselves to be more susceptible to cutting speed of the bit [source; PDF].

IV. Why 6013 Alloy Aluminum May Make More Sense

I suspect that Apple may pick a stronger 6000 series aluminum (namely 6013) over a 7000 series option (with the most likely candidate there being 7075) due to three key factors:

  1. Market readiness
  2. Cost
  3. Corrosion

When it comes to market readiness, there’s already a higher strength 6000 series alloy that’s iPhone ready — the 6013.  Alcoa Inc. (AA) is supplying Samsung Electronics Comp., Ltd. (KRX:005930) (KRX:005935) with this alloy for the Galaxy S6 (GS6) and GS6 Edge.  Alcoa markets its brand of 6013 under the name “Power Plate”.  A press release to the ASM Heat Treating Society reads:
Alcoa, Pittsburgh, is supplying a high-strength aerospace-grade aluminum to Samsung for its latest smartphones — the Galaxy S6 and S6 edge. The 6013 Alcoa Power Plate is 70% stronger than standard aluminum, enabling a thinner, lighter, sleeker design. Developed by Alcoa Technical Center metallurgists, the alloy combines high strength and corrosion resistance for products that require superior durability. Smartphones with metal frames are expected to grow almost 250% by 2016 from 2014, creating stronger demand for aluminum to protect mobile devices.
Samsung’s GS6 employs malleable metal frame (aluminum 6013 alloy).  It further reinforces that high-strength frame with a backplane of super-hardened glass.
PhoneArena contrasts this to the alloy currently in use in the iPhone, writing:
It turns out that the new Galaxy S6 and S6 edge use a grade 6013 aluminum alloy, while most other smartphones, including the iPhone6/6 Plus, make do with a derivative of the inferior 6063 grade. While 6013 is not the highest end 7075, it is in-between, and is still used to make things that need to be light and durable, like plane fuselage, cars, yachts, mountain bikes, and so on. In fact, the 6013 aluminum is 1.5 times stronger and 1.2 times more scratch-resistant than the type of aluminum used in the new iPhones.
Consider, Apple’s assertion that the 7000 Series alloy in the Apple Watch was “60 percent stronger than most aluminum”.  When you consider that you can get 50 percent stronger by moving to 6013, suddenly it’s clear the gap between 7075 and 6013 isn’t as strong as it might seem.

Aluminum 6013 alloy vs 7075 alloy [click to enlarge] [Image Source: TWMetals]
Spot prices on extruded 6013 aluminum alloy are around $1,000-3,000 USD/metric ton [source].  By contrast, extruded 7075 aluminum alloy costs around $5,300-$6,300 USD/metric ton [source].  So the price of 7075 is about double the price of 6013.  For the tiny body of the Apple watch that’s no big deal, but the for the iPhone which has a modest frame size, it’s more cause for pause when you’re producing milliions of units.

Perhaps more compelling though is the supply.  Of the two extruded bar suppliers I spotted of these alloys, the 6013 supplier could produce 3k metric tons per month, where as the 7075 supplier could only produce a little less that 1.4k metric tons per month.
Aside from the Apple Watch, KGI Securities’ confidence that Apple is embracing a 7000 series alloy stems from a comment Catcher CEO Allen Horng gave to investors and journalists.  He commented on June 10 to the Taipei Times:
Thanks to the smoother production and strong orders for metal casings for new projects, we now forecast the next quarter will be better than this quarter.  [Catcher is working to scale for a major smartphone client] a surface treatment on a harder metallic material [that is] is more difficult than traditional metal-casing processes, and would lower the yield rate at the beginning of the production cycle.
The widely held belief is that he was referring to Apple.  But notice that his comment could apply to either 6013 or 7075 alloys.  Adopting 7000 series aluminum might be more buzzworthy and sound cooler than adopting a successively strong 6000 series aluminum.  And go with a 7075 alloy would likely increase strength by a third more than the 6013 alloy found in the GS6.
Bars of extruded 6013 aluminum alloy are seen. [Image Source: Alibaba]
But given the price, production, and corrosion concerns, 6013 in my mind is the more compelling option.  So while it would not be a shocker to see Apple opt for a 7000 series alloy, it might be more pragmatic (and likely) that it will go the same route that Samsung did, given the advantages.

Bars of hot-extruded 7075 aluminum alloy are seen. [Image Source: Alibaba]
If Apple does go the 7000 series route, iPhone owners will have to keep a careful eye out for signs of corrosion.  Anodizing (which Apple uses to provide color) does provide a degree of protection against corrosion.  But ultimately the zinc subcomponent of 7000 series aluminum is relatively reactive and may lead to imperfections in the ninth generation iPhone if it is used.

If Apple is really that dead set on find a stronger solution than 6013 alloy aluminum, it might consider simply returning to its strategy of using a glass backface, a strategy which Samsung cleverly adopted with the GS6.  A high-tech hardened glass backplane would likely provide even more strength gains than a 7000 series alloy, without the potential for corrosion issues.

That said, I believe Apple isn’t overly interested in that solution in spite of its technical merits, hence this may be a race between pure 6013 alloy and pure 7075 alloy unibody designs.

Alloy choice aside, KGI Securities also forecast a brighter color scheme, analagous to the Apple Watch.  Namely the current gold SKU may get yellower, while the gray may get a bit blacker.  A rose gold color is rumored to be added.  The research note also states that the device will carry a new 12 megapixel camera sensor (vs. the 8 megapixel sensor in the iPhone 6+).  It should be interesting to watch how many of these predictions hold true when the ninth generation iPhone is officially announced over the course of the next several months.