In reverse of last year, when we were discussing shutdowns and lower sales, this year's second quarter, we delivered a strong $2.2 billion in sales representing a $1.1 billion improvement as our customers continue to see strong market demand and in many cases, outpaced production as supply chain challenges continue to hamper their operations.
Our adjusted EBITDA for the second quarter was $233 million, a $238 million improvement over last year.
Adjusted free cash flow was of slight use on the quarter, but was an improvement of $120 million over last year, driven by higher earnings.
Diluted adjusted earnings per share was $0.59 for the second quarter of 2021, an improvement of $1.28 per share compared to 2020.
ARFF is capable of achieving 28% improved acceleration when fully loaded with the new EV technology.
As an added benefit, the Striker Volterra vehicle results in 0 emissions driving during entry and exit of the fire station ion EV mode, so that there's no longer a need for expensive ventilation systems, within the station.
The Volterra pumper is serving frontline duty at Station 8, the city of Madison's busiest fire station.
To date, the city of Madison has responded to over 500 active emergency calls with this new electric pumper.
That is why earlier this month, we announced plans to reduce our annual Scope one and two greenhouse gas emissions by at least 50% by the year 2030, which is a five year pull ahead of our original target of 2035 that was announced last fall.
In the second quarter of this year, sales topped $2.2 billion, delivering growth of over $1.1 billion compared to the prior year.
Adjusted EBITDA was $233 million for a profit margin of 10.6%, which represents a dramatic improvement over last year's nearly breakeven results, even as this performance is hampered by dramatic material cost inflation and continued supply chain challenges.
Adjusted net income in the second quarter of this year was $86 million, $185 million higher than the same period of 2020.
The diluted adjusted earnings per share was $0.59, $1.28 improvement from the prior year.
And finally, adjusted free cash flow this quarter was a use of $13 million, an improvement of $120 million over the second quarter of last year as higher profit more than funded increases in working capital and capital expenditures to support the growth.
First, overwhelmingly, the increase is attributed to the organic growth of nearly $1 billion, as our business laps the trough in sales caused by the onset of pandemic-containment measures last spring and summer.
The incremental conversion of 26% exceeds the decremental conversion from the same period in the prior year by about 200 basis points.
Second, foreign currency translation increased sales by nearly $90 million as the dollar weakened against a basket of foreign currencies, principally the euro.
Gross commodity cost increased by $70 million, and we recovered $45 million of this in the form of higher selling prices to our customers for a recovery ratio of about 65%.
These increases compressed our profit margin by approximately 180 basis points and represented the primary impediment to achieving 12% margins in the quarter.
Free cash flow was a slight use in the quarter at $13 million.
This was a substantial improvement of $120 million compared to the same period last year and was entirely attributed to higher profit, which more than funded the higher capital requirements to support the increased volumes.
This represents a $250 million improvement from the previously indicated midpoint of the range and is driven by higher commodity recoveries, stronger foreign currency exchange and higher demand across all three of our end markets.
However, we still expect profit near the midpoint of our range, implying a margin of between 10.5% and 11% as the additional contribution margin from the higher demand is offsetting the higher commodity cost net of recoveries.
This also implies an adjusted free cash flow margin of approximately 3% of sales.
Diluted adjusted earnings per share is expected to move toward the higher end of our range at $2.45 per share due to lower interest and income tax expenses.
First, organic growth is now expected to add nearly $1.6 billion in sales, including our new business backlog of $500 million and the slightly higher end market volume increase mentioned on the previous slide.
Incremental margins are expected to remain strong in the mid-20s, providing about 350 basis points of margin expansion.
Next, we anticipate the impact of foreign currency translation to now be a benefit of approximately $150 million to sales and about $15 million to profit, with no impact to margin.
Finally, we now expect gross commodity cost increases approaching $250 million as steel prices have continued to rise.
We anticipate recovering about $180 million or 70% of the increase from our customers in the form of higher selling prices, leaving a net profit impact of $70 million, which will compress margins by more than 100 basis points.
We expect full year adjusted free cash flow of about $275 million, representing an improvement of more than $200 million compared to last year.
Please turn with me now to page 18 for an overview of the debt refinancing we completed in the second quarter.

Summary:
Diluted adjusted earnings per share was $0.59 for the second quarter of 2021, an improvement of $1.28 per share compared to 2020.
The diluted adjusted earnings per share was $0.59, $1.28 improvement from the prior year.